MPXA4115A picbasic code

[ScaleRobotics]

So you think I have to stick to my already made pcb and don't try an 20 MHZ crystal.

I think your design is feasible. There is no harm in designing the board before the firmware is completed. But there might be some harm ($$$) if you have them made before testing. I would recommend that you wait till you write your PWM sensing and generating code, and test it, before you decide on a final layout. On a breadboard, adding a crystal is easy, if you need to...