If I do anything to my Box Stock Ar15A3 heavy barrel carbine (Model #6721 I THINK), I am wanting to do the following.

1. Add BUIS to take the place of the factory detachable carry handle/rear sight. Which ones should I look at.
2. Replace the factory hand guard for a new one with picatinny rails.
3. Add a vertical fore grip to the new hand guard.
4. Add a light to the rail or get one built into the fore grip.

Now like I said, this is a stock Colt carbine. What else should I consider/do to make it as dependable as it can be? I don't want flash/fancy gimmicks, just dependable functionality.