1. That rifle is more than likely much more accurate than you are. Bushmaster swears their rifles (including 16" carbines) will shoot 1" at 100 yards. Maybe a little exaggerated, but I see no reason why it won't shoot AT LEAST 1.5". Practice and see what you can do.
2.A2 sites are good. If you want a scope, check out Trijicon compact ACOGS. A bit pricey, but well worth the money and can be reasonably priced on the for sale boards. You can also easily mount holosights or red dots with the right mounts.
3. It's a chrome bore, don't worry about it.
4. I like the boresnake myself. And Breakfree CLP. Also, a USGI cleaning kit is a must as well. They can come in very handy.
5. Mags, ammo, mags, ammo, mags, ammo, mags, ammo, mags, ammo, mags, ammo...............
Good luck and welcome to the club!