Ooooh! I know most of the answers...

I just went through this one myself. First off, I don't know what diameter RRA uses, but I'd guess commercial. 2) Yes. 3) No. 4) make sure your stock is the same diameter as the buffer tube. Milspec diameter is 1.14, commercial is 1.16. A commercial stock will fit on a milspec tube, but it will be loose. It doesn't work the other way around. Also, there are numerous buffer tubes on the market, with varying numbers of holes (usually 4-6) for the stock positions. There are also buffer tubes (usually milspec) that have an angled end on them.
A castle nut wrench is handy, but I've done it by being creative, too.

Be aware of all the springs that lurk in an AR stock, my friend. Once you've loosened the castle nut, (after you've removed the buffer spring and buffer, of course), and you begin to unscrew the buffer tube/stock, watch for the spring that's under the buffer tube stop pin - keep pressure on that pin as you unscrew the stock, or it's a missile. Also, on the lower right side of the rifle's lower, where the stock meets the lower, there's a spring and a pin inside there. This presses against the rear takedown pin, and is very, very important. And small. And springy. And hard to find clear across the room.

Good luck!
jr