I built my first trainer...but thats just because I was stupid and had my dad there helping me. Then it crashed and i was like 'screw it' im buying an ARF. I think buying an ARF is a better choice than the RTF. Like piperchuck said in an earlier post, you learn about installing radio, and engine, etc. I know I didnt worry too much about whether or not I made a mistake. If you follow the instructions its hard to go wrong! And ask lots of questions!

Also, since you are a new pilot and all, I wouldnt go with a low wing plane. I would start off with a normal trainer. I had the Avistar and I LOVED it. It can do lots of different manuevers and what not. I think I even half-ass knife edged it once. After you become confortable with the plane and your landings and take off's...then go into a low wing plane, but maybe one with a bigger airfoil like the Sig Somethin Extra, or even the Hanger 9 P-51 you mentioned.

Best of luck to you and ask any questions you may have in the future.

Bobby