Couple of thoughts for you:

Head on over to the 1/2a forum and root around for building ideas and such - a 43" WS P-51 will seem huge by comparison!

Unless you're planning to setup flaperons you may only need a single servo for ailerons if you use a torque rod setup. I've done this in several HOB kits.

The specs on the SG90s look good, but I've never used them. Hitec HS-81, HS-82 or HS-85s would also work well.

EG