Hi Mike.

It depends on you're level of skill flying the trainer. I started flying RC in November of 2004 and started building an Extra 300S Great Planes .40 kit mucho before I learned to fly. If you are confident and comfortable with your trainer, I'd say go for it. They are great airplanes, , but you have to be careful not to slow them down to much, most have a high wing loading, especially in the smaller sizes. All of the planes Ken listed are also good second planes, but it depends on how you are flying your trainer. If you think you can, go for it, follow your dreams man. Typical tools needed for building a kit would be;

Hobby knife (many Extra blades)
5 & 30 minute epoxy
thin and medium CA
sanding block
drill
pliers, wrenches for nuts and bolts, etc.
covering iron
heat gun
loctite