Some people use hollow or solid core doors for the top of their tables. Occasionally Lowe's (or other supplier) will have a damaged door that you can buy at a huge discount.

If you download one of the trainer (PT-40 or PT-60) manuals from http://www.greatplanes.com/parts/index.html#kits it has some suggestions for building a table. You can adapt their ideas to accept a door or mdf table top. Keeping the surface supported so it stays as flat as possible is the main goal. Some people put threaded adjusters under the tabletop so they can compensate for imperfections.

From what you've written, you will have the patience to take your time on the build. As long as you understand each step, and even look ahead to see how it impacts a future step, you should be able to build the P-51. If you built a few simpler kits first it might make this build easier, but there is no reason that you cannot build the plane you want.

The Great Planes 40 size Corsair was my third kit (after a PT-60 and Uproar 60) and building the gull wing was quite a challenge. It sort of "burned me out" and my brother built the fuselage and finished the kit for me.