When using acrylic, I highly recommend using a 1/16" or 1.5mm plate, with a thicker acrylic plate directly below it (with holes cut a little bigger). If you’re direct wiring, the second plate can be like 1/4" or 6mm or even thicker; if you have a PCB, then there’s a limit to the combined thickness of the two plates (I think ~4.5mm, but I’m not precisely sure).
Using two plates like this lets you get something that clips the switches in quite well, while also being pretty sturdy.
If making a plate for Alps switches, either 1/16" or 1.5mm will work as a plate thickness for the top plate, but the size of the hole should be a little different depending on plate thickness.
If making a plate for SMK (“monterey blue” etc.) switches, then anything over 1.5mm is too thick for the top plate (1/16" is ~1.6mm).