It's only as settled as you make it; the interior and the borderlands between Many-Arrows and the Silver Marches are relatively settled, yes, but at least in my game when you head north or head west you find a wild and rugged untamed land. It's a kingdom in a constant state of war against tribes of giants, goblinoids, and human barbarians that surround them, where monster hunting- and dragon hunting, with the spine being full of dragon lairs right from the picking- is one of the more popular and profitable professions. Exploration into the local underdark is another big part of it- Many-Arrows sees all the land within it's boarders as it's own, even what's underneath the surface.
Even in the interior, in Dark Arrows and other well settled regions there's room for intrigue; politics between rival tribes vying for power- much more straightforward than the schemes between drow families and human nobles, but no less cut throat. Another issue is the ethical issues regarding the slave trade and treatment of prisoners of war. Also present are business rivalries between mining or ranching operations(if you don't think these can be exciting you need to watch more westerns). Which of course is to say nothing of religious disputes between the old, more traditional orcs and the new, more progressive orcs and their rival gruuman cults- beyond being in a perpetual state of war with it's neighbors, it's in a perpetual state of holy-war with it's self.
One of the things I did in my campaign when developing Many-Arrows is that I eliminated the racial homogony of the area; while it's still 65-70% orcish/half-orcish, it has a substantial population of humans, dwarves, duergar, genasi, shifters, goliaths, ogres, trolls, and goblinoids, with smaller groups of dragonborn, drow, minotaurs, and tieflings.
Human and dwarven citizens of Many-Arrows come from two main sources. The first would be fugitives fleeing justice from the south deciding that Luskan was becoming simply too much of a dive and a risk, and that it may not be far enough away from their problems to escape. The quarantine that the city would be put under during the novel Shadowbane would also motivate more fugitives to head further north towards the Spine and Many-Arrows.
The other source is enterprising, progressive orc tribes bringing in human and dwarven mercenaries to support their troops, and in some cases even train their warriors to combine orcish savagery with human and dwarven military discipline. Aside from these sources, plenty of humans are the result of the orcs raising orphans left from their battles with the Uthgart tribes of the area.
Duergar in Many-Arrows are a callback to an earlier campaign I was in(but wasn't dming) that involved a semi-nomadic community of exiled duergar that, over the course of their campaign, were driven from their settlement. Later, with the permission of the dm of that game I transplanted that community to my Many-Arrows settlement, with the story that they had wandered through the underdark looking for a place to settle and finally came to an agreement where they would help work the metal from Many-Arrows' booming mining industry(a plethora of untapped ore veins in the spine ripe for the taking, which was another big draw for immigrants) into armor and weapons in exchange for military protection from underdark threats and citizenship.
Genasi come from a few different places- most of them are earthsouls and windsouls who were already living in the region and decided that it was better to inergrate with the orcs than fight them off like the human barbarians. Others migrated here- some mercenaries brought in with the humans and dwarves, some fugitives on the run, some Abeirnians(and this applies to most of the dragonborn as well as some humans and half-orcs) were drawn by the promise of dragons to hunt in the wilds of Many-Arrows, and weren't disappointed. Others, mainly stormsouls, came due to an attraction to certain religious movements in Many-Arrows that I'll cover later.
Many-Arrows' shifter population mainly comes from right across the river in Glimmerwood; the People of the Black Blood, shifters and lycanthropes alike deciding to migrate into Many-Arrows for the promise of religious freedom and considerably less restrictions on Malar worship than they were receiving from the elves. Like the human mercenaries they were recruited by clever orc chiefs to bolster and diversify the ranks of their tribes, adding lycanthropes and druids to their arsenal.
Goliaths, like genasi, were mainly indigenous to the area; a lot of them had a certain amount of respect for the orcs, their strength, their prowess and fearlessness in battle, and in turn the orcs respected the goliaths for their power. The integration was easy, with goliaths finding easy utility within orcish society.
Goblinoid citizens(distinguished from members of goblin tribes that reside within Many-Arrows' boarders but are actively fighting against the Kingdom) are primarily the descendants of tribes who were either conquered or who willingly came over to the orc's side to avoid annihilation.
Most dragonborn who live in Many-Arrows were members of those human or dwarven mercenary bands who were brought in to fight and train, or came seeking dragons to kill in the Spine, and found they fit in well with the society and decided to stay.
Drow in Many-Arrows have a complicated place in society; in my games the nation has come under attack by drow several times, both overt and covert, seeing an united kingdom of orcs as too big a threat as it could potentially serve as a beacon for their slaves to rise in revolt. And that's not an unfounded fear as one of my campaign plots involved agents of Many-Arrows infiltrating a drow city as slaves aiming to do just that to bolster it's own population and weaken the drow threat. Still, most orcs recognize the part Drizzt played in helping to found their kingdom(grudgingly or otherwise) and many of Obould's hero-cults look at Drizzt as having been a worthy opponent for their patron, which affords some measure of respect towards those drow who are renegades fleeing their society. Such individuals are also expected to provide some services towards Many-Arrows, whether it's providing them with intelligence relating towards drow or other underdark threats, with magic items of drow origin, or serving as spies or instructors for Many-Arrows' armies.
Minotaurs I admit are just kind of thrown in here, but they're one of the 4e player races that just aren't well integrated into the realms in a way that lets them interact as social creatures rather than monsters. Many-Arrows is as good a place as any to throw them.
Another aspect I've applied to Many-Arrows in my homegame is near complete freedom of religion- elven deities are the only ones that are completely outlawed(Lolth included). There's very little in the way of organized religion; some cults are more organized than others, but with a couple exceptions there's nothing that could be called a church or a clergy. Still, most non-orcish faiths are required to pay some form of tribute or homage to the more numerous and powerful orcish cults that tolerate them. All of the Nishrek gods are worshiped prominently here; Luthic, Bahgtru, Ilneval, Obould, Shargaas, Vaprak, and Yutrus, though all of their cults acknowledge Gruumsh as their chief.
One of the biggest religious movements is what I call the Cult of the Storm That Never Sleeps, or the Cult of the One-Eyed Storm. They're a cult that variously believes that Gruumsh either killed Talos during the Spellplague and assumed his mastery over storms, or (in more fringe cases) believe that Talos was always a mask worn by Gruumsh. The cult extends into primal worshipers among shaman and druids who revere Gruumsh as a spirit of the storm and destruction, but over all the cult's take leans towards an unaligned view rather than a chaotic evil one, worshiping Gruumsh as a god of power and strength, his destruction a force of nature rather than an act of cruelty or malice. They also see him as a force of freedom and change, destroying one thing to make room for the next, as well as a fertility god- his lightning may cause forest fires, but the ash from that fire enriches the soil and lets new life grow. Non orcs who worship Gruumsh likely belong to this cult, especially stormsoul genasi. This cult is one of the bigger enemies of both the traditional worshipers of Gruumsh as well as human worshipers of Talos. One of the main inspirations for this cult was the Lightning Blitzer paragon path detailed in Dragon Magazine #386.
Asmodeus worship and devil worship in general is openly allowed in Many-Arrows, though independent cults are watched closely. Asmodeus worship was brought here by the duergar, who worship Asmodeus as their liberator from the mind flayers, as their protector, as a great warrior, and master schemer. Such beliefs were often passed to the orcish apprentices of the druegar forge masters, allowing devil worship to spread. While Asmodeus is the most popular object of worship among devil worshippers in Many-Arrows, small cults to the other archdevils exist- Bel enjoys considerably more popularity here than perhaps anywhere else in Toril, being a warrior's devil suits him towards the orcs and goblinoids tastes. Dispator is right alongside Gond as the go-to patron for duergar and orc architects who design or otherwise improve on the many fortresses and strongholds throughout the kingdom. For mercantile matters, Mammon's cult is more popular than Waukeen or Graz'zt. And in matters of the forge, many Duergar name Belial their patron as their forging techniques are those of the Phlegethos, the Fourth Hell. Fiernia and Glasya also have small cults in Many-Arrows, though they're mainly devoted to carnal pleasures, and Levestius, Baalzebul, and Mephistopholes have no real cults to speak of.
Among humans, by far the most popular god worshiped in Many-Arrows is Tempus, patron to many a mercenary and adventurer who immigrated here. Worship of Garagos is almost unheard of here, with Gruumsh occupying his role. An interesting cult of Tempus worshipers, primarily human though including other races, has popped up, though no official name has been given to them. Their message is that Tempus and Gruumsh are battle-brothers, worthy rivals who've fought alongside one another against the enemies of the gods. While this cult hasn't gotten much momentum, it has done something to help improve human orc relations, though the local barbarians see it as an affront. The Red Knight is another popular choice among the mercenary population, especially those hired specifically to educate orcs in military strategy.
Among the dwarves, Moradin of course is the most popular god, here like anywhere, though worship of him tends to be downplayed as it causes tension with the orcs and most dwarves know they're here at the orc's suffrage- this earns them the resentment of dwarves to the south for caving to orcish demand, but they worship regardless. In public, Vergadain tends to be the most popular dwarven deity, followed by Clangeddin Silverbeard and Thard Harr.
Bane and Maglublyet maintain decent sized cults among the goblinoid population, though most of them have converted to Gruumsh worship, at least publicly. Bane does maintain cults among the humans who've immigrated here, largely among the more ruthless mercenaries who choose the Black Hand over the Lord of Battles. Still, most in Many-Arrows are too wild for Bane worship, and his cult does little in the way of recruiting here.
Auril, Akadi, Grumbar, and Kossuth(in that order) are also popular objects of worship in Many-Arrows, primarily among genasi, but all orcs who live in the cold mountains pay some homage to Auril, Akadi, and Grumbar, and Kossuth is popular among orcs who seek to use fire as a weapon.
Malar is the most popular patron of shifters, lycanthropes, and rangers in Many-Arrows, surpassing Silvanus or Mielikki(though both do have worshipers here). Likewise, Talona enjoys some popularity here, her cult closely allied with both Luthic and Yutrus.
It's not all evil, of course; Amaunator, Torm, Ilmater, Milil, and Sharess all enjoy small, growing cults here, with several orcs expressing interests in them to various degrees and for various reasons, though the actual number who have accepted these gods as their patrons is extremely small, many do pay some homage to them.
...That's about...little more than half of the work I've done developing Many-Arrows. Sure, granted, pulled a lot of that out of whole cloth for my campaign, but if I can do it I'm sure someone who gets paid to do this for a living has the creativity to really delve into it.