Gotta agree with the rest. Something along the line of a 4*, venture, and so on. I personally like the Super Sportster 60, a pretty rugged plane that has good sport flying qualities. What you need to learn with these types of kits is building sequence, what wood to use where, what glues to use where, covering, equipment installation and high stress points. Kits of this class generally align themselves pretty good but it wouldnt hurt to learn how to do alignment checks on the firewall, wing/stab incedence and fin offsets. At some time you'll run across a plane that just doesnt seem right even though you're sure its built right. Usually one of the alignments are off. (Not all kits are created equal) Keep a close eye on hardware quality. As time goes on you'll develop your own way of doing things (which usually wont be too different from a lot of other builders).

I would highly recommend you put the warbird off till later. But like Chuck says, the GP P-51 kit shouldnt be too bad based on its reputation from people here on RCU. I have no actual experience with it though.

Edwin