For the metric to imperial conversion, it only affects the thickness of the acrylic, the design files are just vectors so aren't affected.
There's a page on the Ponoko website that details the thicknesses in both metric and imperial https://www.ponoko.com/make-and-sell/sh ... ylic-clear
That page explains that the thickness can vary (even within the same sheet in my experience), but I've laid out the parts in the design file so that everything is close to the other parts that need to be the same thickness.
The 3mm sheet is equivalent to the 0.118 sheet.
I've suggested using the 0.220" sheet in place of the 5mm sheet, it's a bit thicker but will ensure there's enough clearance (it'll only be 1mm thicker overall).