Hm... well a few more things come to mind.
As someone who has use Stormtroopers as allies before, yes they're cheap, yes the special weapons come in handy, but man do they preform miserably when compared to space marines. Might be better to replace them with scout squads, but yeah I get it.. fluff thing.
So if you're adamant about keeping them, here is about the one place I *wouldnt* suggest a sarge with a fist. Namely because I think the squads are going to get eaten alive in close combat whether you have one or not. I've also never been a huge advocate of the grenade launcher. It's just... eh. Flamethrowers, meltaguns, plasma guns... just about any other special weapon would be a better choice.
Your elite devestators are a bit expensive, at ~250 points for 8 models. A lot of it is that a guy with a bolter is costing you 21 points. I guess I'd suggest either dropping one of the veteran skills, or cutting each squad down to 6 models. You loose two meat cushions, but you save points. I dunno, either way they'll probably be target priority #1. They'll last longer with the extra 2 models, but you're also giving the other guy free vic points for every marine with tank hunter/infiltrate that he's not really using effectively.