You should start with a slow, gentle plane like the Eagle, Kadet, Tower Hobbies Trainer, or any of the Hobbico trainers. There are others. ANY P-51, even one that's on teh market now, labeled as a "trainer", is NOT a good plane to start with. No matter how you modify a P-51, it's still a P-51, and will act like one.

If you like warbirds, your natural progression of planes will be:
High wing trainer
Low wing sport plane
Warbird

I know you want to jump right into the warbirds, but save yoursaelf some grief, time, and money and take it slow. You gotta walk before you can run.

Dr.1