For weight, you can start by using lighter materials, like the plastic pneumatic tanks or 1/16" aluminum extrusion. You could also sacrifice your swerve drive and switch to the lighter 6/8 wheel tank drive design (which would be sad because swerve is cool). I also really like
this paper which is about lightening a robot after it's built, but still has a lot of tips that are valid in the design process, too.