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Some giant colorless things would probably be good with the Paincast ability.  Wurmcoil Engine is free whenever Rakdos connects, and the Eldrazi are always fun .

You missed Shadowblood Ridge and Tainted Peak , as far as lands go. Sulfurous Springs , too, although I can understand skipping the painlands.  Jund Panorama and Grixis Panorama are more fixing. Molten Slagheap isn't exactly fixing, but it does have some utility.

I think 24 creatures is a little low for EDH, unless you're running something that works well with few creatures like Rafiq , Uril or Zur
I'd run bigger creatures, this is EDH after all. Scythe Specter instead of Guul Draz Specter for example. Rakdos ability actually helps you cast bigger creatures. 

You should run things that deal damage to everyone, like Exsanguinate . Say you are playing against 3 opponents. If you cast Exsanguinate for 3, you make them lose 9 life and then cast Artisan of Kozilek for free.

I was thinking about this guy. I'm not sure yet if he's 'good', but he's certainly potentially powerful and a very interesting deckbuilding challenge.

Let's break it down.

1) He needs same-turn damage in order to be cast.

Opponents damage themselves (eg: fetchlands) and each other all the time. So vedalken orrery probably takes care of that when you get to play it. Winding canyons too...but at that point you're tapping 7 lands to play him so canyons iss not actually that helpful. Orrery's kinda good for these colors because they're heavily sorceried....but it's only 1 card in the deck. You *could* play burn effects for the damage, but you don't really want to be paying extra mana and throwing away extra cards just to cast your general. So we want repeatable/delayed sources of damage that we can rely on and that can hit the board before rakdos himself. Cheap evasive damage-dealers like dauthi horror , bitterblossom and shepherd of rot don't generally care what's on the board while getting damage in. And they'll help increase the discounts offered by rakdos after he's in play. Utility bodies like pilgrim's eye , phyrexian rager , imperial recruiter , and goblin welder can get rakdos online quickly as long as at least one player lacks blockers, and still give some value aside from that purpose. I think you need a lot of cheap (yet worthwhile) creatures and damage sources to ensure reliable access to rakdos, because let's face it...you have to be aggressive. Other colors are going to be better control decks than you, and the discounted mana costs offered by rakdos lose their lustre as the game wears on.

So let's assume you've included a sufficient quantity of cheap repeatable damage to reliably get rakdos online. Now you have to consider

2) How you're going to benefit from his discount ability.

There are cards (like earthquake , heartless hidetsugu , exsanguinate , etc) that can turn the discount monstrous. And if you find a maga, traitor to mortals in your hand...well that's a pretty big game. But there aren't many creatures like maga that can really take advantage of a -24 mana cost deduction. And keep in mind that rakdos himself is a 6/6 flampler, and whatever damage source allowed you to cast him can probably work again. Hitting with a 2 power shadow guy and flying in for 6 with rakdos lets you play Ulamog for 3 mana, or blightsteel for 4...and that's more than good enough. I don't think you need to build the deck around 'going big'. Just include a sufficient number of fatties to reliably have 1 or 2 big follow-up plays once rakdos goes live.

So now we've got a gameplan. We want early critters that are either evasive, or just chumps that can give value. We want so fat to make use of rakdos's discount. And including sufficient quantities of both to make this gameplan consistent will probably take up the bulk of our deckspace, and the bulk of our early turn development.

Interestingly, I think this is one deck type that doesn't really care about mana acceleration. At 4 mana, rakdos already IS accelerated...kinda. What you need isn't a signet to speed him up further, you just need ways to deal damage (without costing mana that turn) so that you can cast him period.

I'd still probably include maga and a few earthquakes...and some tutors to help make it happen when you get the opportunity to go for it. But that's not something you expect every game... More realistically you're just trying to go turn 2 dauthi slayer turn 3 cunning sparkmage , turn 4 rakdos, turn 5 swing swing ping, myr battlesphere + wurmcoil engine + bogardan hellkite . And hopefully you have a tutor to find necropotence or wheel of fortune or memory jar or whatever to keep the beats pumpin'. The card draw options in these colors are few but powerful, and you want pretty much all of them ( dragon mage ? Yeeeeah!)

For the long game I was thinking on repeatable non creature damage sources. Rod of ruin, or arc blade, pestilence and pyrohemia (kinda).

Along the line of lands, Leechridden Swamp is useful for causing opponents to lose life. I once used that with Sanguine Bond and Exquisite Blood in an "I hate everyone else at the table" B/U deck, and didn't realize it until everyone complained that I had an instant win. But hey, it worked!