as suggested, get to a club and speak with the people there, if you turn up with a big .46 gasser and they are flying park flyers your going to look like a bit of a plank :P

also id recomend a high-wing trainer, high-wings have self-righting charecteristics and are very stable and easier to land/takeoff with. afterall, the P-51 is still a warbird no matter how many gadgets they put on it

get yourself a decent trainer such as the tower hobbies .40 trainer, a SIG kadet Senior or another decent well-built trainer, a reliable .40 or .46 engine (depending on how big your bird is) such as the OS .46LA, then a good quality radio set (Futaba 6EXAP is £120 and has RX, battery, switch, servos and everything you need to get going radio-wise) and that should about do a quart of 5% fuel and organise a time at your flying field when you can get a senior member/instructor to check over your plane and then your on your way! :P