1. I know I suggested it in your other thread, but I really like the 3 point Blackhawk! slings. For two point slings, I hate them, but I do really like the standard military style sling with the J hook. It's quickly lengthened and shortened, and can be adapted for hasty and loop slings. Seems decently durable also. I've had other two point nylon slings and they were harder to adjust and weren't as versatile.
2. I've got a Rock River Arms free float. I would go free float if you've got the tools and know how, or an honest gunsmith nearby. The hand guard itself is cheaper, and will help out slightly with accuracy since the sling pull or rest on the hand guard won't affect the barrel.
3. I've got an ACOG (army style with the hand adjusters) on mine, and it was pretty dang expensive. Really can't give any first hand input on cheaper models. I have heard a lot of good things about aimpoint though.
4. There's a lot of 'em out there. I think the most important thing is that it doesn't have any play when mounted. Secondly, get one that feels good in the hand. Brand really isn't that important.
5. Lights you can never go wrong with a surefire. I've been using SF's for years, but I do have an Insight Procyon on my pistol and am quite happy with it...it was a lot cheaper than Surefire, but the performance is on par, so if you can find something from Insight, it's definitely worth checking out.