1/4” plywood makes surprising good box making material.
Table saws are way too dangerous for making 4” x 2” boxes. Use a band-saw instead.
Freehand sanding using the disk sander works, but you have to be careful or your parts will not end up square. Unless you really want a slanted top to the box, make sure you use a fence or square.
The large band saw blades leaves a lousy edge, but the disk sander fixes that quickly.
Even a fine grit disk sander quickly takes off a lot of material, so be careful.