Right off the bat the Elemental Initiate theme offers you an implement solution in Ki Focus proficiency. Even if you go with a different implement later on it's still a damn solid path.
Given you're partial to being on the frontlines, I might also toss out a recommendation for Battlefront Leader instead of Combat Leader. That heavy shield it gives could be quite a bit of help.
Combat Leader is locked in long term for Combat Commander, since Team PC getting +CHA to initiative is huge. Can you retrain that? I'll grab Battlefront for better survivability now if you can retrain that feature though, +2 initiative doesn't come close to +2 AC, +2 Reflex.
Long term though, I'll be grabbing Sidhe Lord theme and using either AIP or Pact Blade Rapiers to fix my Weapliment issues. Sidhe Bargain is a solid enabling power since it grants a full standard, but mainly it lets me abuse Flame of Hope even harder.
Powers do look good.
Theme + Background is the way to go. Auspicious Birth/Born Under a Bad Sign will get you some significant extra hp. Normally I'd suggest MC Executioner for Ki Focus + 1/enc damage boost + 1 skill + access to Cursed Shadow, and then say to grab a Blazing Arc Ki Focus and take the Infernal Prince Theme. Since you plan on going MC Invoker for Flame of Hope, I'd say take Elemental Initiate for your theme. As mentioned by Planeswalker, Ki Focuses are probably the best answer to your weapon/implement split.
For the rest, I'd personally go 20 Cha and take HT: Warlord Armor Proficiencies for chainmail + light sheilds, and rock a rapier while shooting for Deft Blade in Paragon. Then an expertise, Imperial Majesty, and either Deadly Draw or Hellfire Blood if you did end up with a Blazing Arc Ki Focus.
Liking some of the Ki Focuses, Rain of Hammers (minor action Eldritch Strike) and Ghost Mask in particular (why yes, I would like to be damn sure to hit with this, thanks). I just don't think I'll have the feat space for full Fire op needed to make Blazing Arc really good, but Hellfire Blood is still a point of accuracy on every damaging melee attack, which is still pretty nice.
You're right about Rapiers over Longswords though, they're a better weapon for me due to generally better support options (Deft Blade is awesome, Pact Blade Rapier can buy me a feat). Not as keen on Chainmail since it's not any better than Leather AC at 8th level with the INT boost, there's absolutely no Warlock support there and I've seen the lost speed matter enough times. I could take Warlord Armor Prof for Shield since Leather+Shield = Hide AC (while still allowing Armor of Dark Majesty for Plate AC vs. Cursed enemies) and retrain for the Presence once I need it for a powerful rider (say Inspired Belligerance).
Probably going to switch feats up to Versatile Expertise, Imperious Majesty, Mark of Healing, Hybrid Talent (Warlord Armor Prof)
If you're planning on going Flame of Hope PP, taking the balanced int/cha array might turn out better. I wouldn't worry about to hit so much, since most of your powers are enable powers and you'll be spamming Commander's Strike quite a bit with your standard actions.
Born Under a Bad Sign/Elemental Initiate is definitely a potent package for you right now since it effectively amounts to +10 HP and solves your weapliment issues.
Yeah, I've realized that half of my accuracy issue is just me comparing this to the op you do on a Controller/Striker, who basically needs to be hitting on 2s, as opposed to just using the Striker's accuracy op (I've never played a Leadstriker, only Binders and Warlocks). Definitely taking Born Under a Bad Sign/Elemental Initiate for now for the Ki Focus, but intend to move to Sidhe Lord as early in Paragon as practical (probably move to either a Pact Blade Rapier or just go for the throat and get an AIP'ed Radiant Rapier).