Are you sure you want 1/4 acrylic? That's more than the distance between the retention clips and the bottom of the switch- switches wouldn't sit on the PCB.
I have an Acrylic plate/case that uses two layers of (I believe) 3mm for the plate layer. It works fine, and completely hides the lower half of the switch, allowing the PCB to snug right up to the switch. I did not measure the plates, but I they look like standard "1/8 inch" Acrylic, which is about 0.110", if I recall correctly. One layer would be too thick for the clips and too thin for a friction fit. Thus nominal 1/4" Acrylic for the plate.
If I use stainless, it will be 0.060" per the Cherry specs.
This question is regarding a hardwired prototype without a PCB, so as long as the leads protrude, the switches will be fine. I suspect Costar stabs will be easier to make work in Acrylic, but I haven't done it myself, and would like to hear from someone who has before I drop $80-100 on a one-off plate.
- Ron | samwisekoi