I think the most important tool you can have is YOU. I've built planes from scratch, using just a few hand tools. Life is much easier with a few power tools to speed up your build, but if you have the patience, even lite-ply can be cut with an Xacto to a tolerable finish.

Comments above about a good set of plans are VERY important also. I've seen plans that came with a Kit that I've later scratch-built a plane from (reason not to be revealed :-) ) where the ribs of the tapered wing are NOT EVEN CLOSE to the right outline. A wing built from them would not even have it's leading and trailing edges match up with the ribs at the proper locations (ribs are tool long or short, too tall or short).

If you are the 'type' to scratch-build, you should make it ok. The 'type' means: you know more glue is not necessarily better, you are aware that a tight joint is INFINITELY better than a loose joint, you strive to insure that the parts are warp-free, you can figure out ways to check the fuse and wing for proper alignment and decalage, you know that the firewall MUST be at the correct angle, you are ready to check and re-check the CG and can easily change the locations of radio and battery to make it correct, and lastly and most importantly, you must ENJOY doing all of this!

Many things to do with scratch building will come with time: better tools, a deeper understanding of the proper size and grade for important pieces of wood in the plane, where to add or remove excess wood, how to know when it's ok to 'fudge' a little, but with a normal build, you will do alright.

Good luck, and enjoy.