All of the videos are useful, I'd make some time to watch them all and take a few notes.
One tip I do have for trimming the Wii tho, is to make your cuts run the full length of the board. Rather than trying to cut the trim section out of the middle of the PCB, cut the entire PCB into smaller and smaller bits. This will improve your control and reduce the chance that the disc might jump. Rotary cutting wheels cut with rotation speed rather than pressure, so use light consistent pressure and let the disc spin fast and move through the PCB slowly. Too much pressure and it'll jump, if you change the angle of the disk mid cut it will jump as well.
Just take it slowly, draw your trim lines with a ruler, and cut a few mm outside the lines to give yourself some margin to sand it afterwards. I'm sure you'll do fine
