I spent another couple of hours at it yesterday, and finished the cutting of the first side, and most of the second side (which was faster). Once the big cuts were out of the way, I moved from the floor onto sawhorses which made the work a lot easier to wrangle. I did use a plunge cut (if that’s what you call it) to do the “monitor edge” and finished the corner joins with a jigsaw. That was quite easy.
Here’s the first side cut and acting as a template for the second side.
My plan is to clamp both sides together and sand them, then rout the slot around the edge for the t-molding to fit into. Which reminds me, I need to order the t-molding.