I find it amusing that when someone makes a post like this in the beginner's forum, the first post is to jump on him, from someone who assumes he already knows the situation, rather than offer some sound advice.

DBcherry has an excellent list of parts.

I personally do not like the small 12-volt batteries for use with an electric starter. I use a 12-volt battery for a small car. It's got a carrying handle and I've charged it once this year so far. I never worry if I'll have the juice to turn my engine over. It is a little bulky, but it's something I deal with.

I would recommend that you get a trainer that you can assemble yourself, rather than an ARF. If and when you damage it, you will have a much better idea of what it's going to take to repair it, and that will carry on to other models like your P-51. Covering isn't too difficult. Takes some tries to get it decent and 100% wrinkle free. As a side note, I prefer H9s Ultracote over Monokote. IMO it goes on better and shrinks up better, and is easier to pull and stretch around curves.

Good luck whatever you choose to do!