Ok, so here's what I believe is the proper sizes for the Ultimarc Trackball. Here's the template I made:

Now am i understanding correctly that I'm going to have to use the router to make a recess of 152mm X 152mm for the cover, so it can go under the plexiglass? Then just use the router to remove the whole 120mm X 120mm square? And the only hole I'll be making in the plexi is for the ball itself, right? What is a good tool for that? Thanks!