[AustinSchuh]

Make the flanges on the front/back of the bot 1.5 - 2" long, and then take the edge and bend a 1/2" flange down from that.

Take another set of the plates that you are using to strengthen the drivetrain tube and put them on the bottom. This will help a lot with strength.

Birch will be fine. You can attach electronics to it quite nicely with some industrial grade double stick tape. The birch will keep your frame square and help prevent the front from bending in when you hit things.