Adding Acrylic Shield to 1000 mm Machine

I know that many have built rather elaborate tables and enclosures for their X-Carve, but we are trying to keep our machine more portable … even though it is 1m X 1m. With that in mind we are thinking of using post-assembly insertion nuts to attach 1/4" clear acrylic shields to the front (and maybe the rear) of the X-Carve to help keep dust and shavings out of the power supply and laptop computers. We would like to use M5 fasteners for this but are unsure of the best length to use. I know 20 mm would be too long, but would 12 mm or 16 mm be the best length to attach 1/4" acrylic to the extrusion?

12mm is just under 1/2" and 16mm is just over 5/8"