Others have covered this info, but I think I can add a bit.
Collapsible stocks:
CMT, LMT and Magpul are going to be your best bets. I chose a Magpul because it is longer than an A2 when fully extended and I am one tall guy. I think where you are getting the "rattley" stock thing from is that some companies make look alike M4 stocks that aren't mil-spec.
Night sights:
I've never heard of someone using them on an AR-15. I have seen front sight posts with a fiber optic running through them, but never on a weapon. Most people seem to get either an Aimpoint or EO-Tech/Bushnell holographic sight. Those are expensive though and you need funky adapters if you are mounting to an upper reciever with a non-detachable carry handle.
Flash Suppressors:
I can't reccomend someone to turn your barrel, but I can reccomend a FS. The Smith Enterprises Vortex and the Yankee Hill Machine Phantom are the current hot items. Both are going to mask the shot enough that it looks like you are flicking a bic. The Phantoms are $25ish and come in 3 versions. The Vortex is $40 and comes in one. The Phantoms break down as follows, model 28 has 4 ports and an agressive muzzle, the 5C1 has 5 ports (for firing prone with no dust kick up) and a smooth muzzle, the 5C2 has 5 ports and an agressive edge. As far as the barrel being heavy, it is probably more than you could ever need, but I wouldn't bother switching it out or changing the profile unless the weight bothers you.
Lighting:
Surefire makes handguard replacement lights, they are about $500 IIRC. You could get a floating foregrip and attach a light too. Surefire, LaRue and Pentagon Lights are pretty good. The combined price is going to be at *least* as much as the surefire handguard lights but you get the advantage of free floating your barrel too. As a bonus, surefire weapon lights have parts commonality with their M series lights.