I was thinking of using the Command Squad to sit back and take pot shots or hold objectives, the two Infantry Squads w/ autocannons to tarpit and objective clear, the Infantry Squad w/ priest as dedicated transport hunters (hence krak and priest to help on assaults), and the Special Weapons Squad as mob killers (lots of orks and 'nids in my neck of the woods).
3 Flamers doesn't scare Orks or Tyranids, who just have to send a couple of Devourers or Big Shootas to either wipe the 5 T3 bodies or send them running on LD7. Guardsmen don't really clear objectives unless they're Veterans in Chimerae with Meltaguns or Plasma Guns. They claim the objectives while the other stuff clears them.
I have already have two biker squads that are great for tank busting (power fist and lightning claw on champion means no attacks lost) so I was just looking to plant the tanks and get dakka down range.
Power Fist AND Lightning Claw on the Champion? They're some expensive 1 wound, 3+ save models right there. Why not 2 Meltaguns? Imperial Guard can do the long-range anti-tank game a LOT better than Chaos, so I'd use that fact.
If I was going to bring a flyer I would bring a helldrake, and I'm not to worried about points because I like the idea of a chaos war band with lots of disposable cultists and the elite chaos marines.
So why are you taking expensive Cultists with unecessary wargear? The Vendetta is probably as good as the Heldrake, dependant on list. If I was against anyone with significant mech presence (all good lists) I'd prefer the Vendetta.
Vendetta is one of the best flyers in the game, if not THE best, so don't dismiss it right away! MidnightSun is probably right about the krak grenades, though I respectfully disagree on the sniper rifles. They're especially good against Tyranids.
Also, gotta bring back the point about the sponsons on the Leman Russ. To me personally, it's not worth paying the extra points for something that'll only hit on 6's. I'd take those points and use them for a power weapon or something for a Chaos Marine. And in my opinion, Leman Russes look much better without sponsons.
I don't think Sniper Rifles are 'especially good against Tyranids'. One wound per turn on a Monstrous Creature is nothing big, really, and for 50pts you could do a lot better.
They're not just 20pts for 6 BS1 shots, though. They reduce the chances of Weapon Destroyed on your important gun from 50% to 25%. Personally, that's enough reason to buy them. In addition, I think you underestimate snap-firing Heavy Bolters. Roll enough dice enough time and occasionally you get freakishly lucky and hit with 3 or 4.