Not much I can add, these guys covered it well. You've got an X-acto knife, buy lots of blades, throw them away often. Razor saw is next most important. And as far as I'm concerned, razor plane, razor plane, razor plane!!! You can't shape balsa properly without an ultra cheap Master Airscrew Razor Plane. And buy some spare blades while you're at it. The other must have item after razor plane is the aluminum sanding block with stick on sanding paper. I have several with different grits.

For T-pins, go to your local sewing store. It'll feel funny but they'll love you for it and you'll get a good price. Support your local hobby shop but for common items use hardware stores or such. I'm a regular at Hancock Fabrics. For glues, do use the local hobby shop. Super glue from the hardware store just isn't suited to balsa like the stuff you'll get at the LHS.

When you find that you're enjoying building and want to build from a set of plans instead of a kit, a scroll saw is a great addition. Actually I find I use my bandsaw more but it's a bigger ticket item.

Build, build, build, before you know it you'll have everything you need. Okay, I lied, I still want more tools.

Dave