Now that the budget is finalized and the CAD is ready, I imported all of the parts that would be used (except for the ones on the PCB) so that they would have the same dimensions as the actual parts, be low-poly, and look similar in Onshape to the real parts. (The main reason this took so long was that I got a little sidetracked and tried to perfectly match the dimensions of the heat-set insert, which was hard since the seller I am getting it from is a somewhat shady, low-documentation vendor.)