A Mustang or any other warbird will not make a good trainer.....Warbirds by their nature are not forgiving airplanes.....they can stall into a snap roll and then a "death sprial" that the most seasoned pilot can't get out of unless he has some altitude.......Unlike cars we can't pull to the side and stop until we reset ourselves.....
Instead I recommend a good high wing trainer like the LT-40, Alpha, etc. that are forgiving aircraft and don't have any bad habits......
Finally get yourself an instructor and learn to fly the easy and cheap way.....Like most things it is better to start out slowly and work yourself up to a Mustang as a 3rd or 4th airplane....go to your local flying club ask questions meet the folks there....the next thing you now you're on your way.....good luck