I would recommend imsto thick grey pbt. Those looks absolutely sexy seriously. I will be getting them soon for my qfr
Edit: there are no holes for functions afaik
They don't come in windowed keycaps, but you should be able to see the red LED through the PBT if it's on.
Okay, just tested. With IMSTO white PBT, you can easily see the LED shine through it. It looks really great, actually. Better (over an LED) than SP white PBT.
Using my gray IMSTO Geek Hack key, I could not see the LED through the keycap at all, but the light was still visible reflected off the plate.
I already know I'll be very happy with my IMSTO PBT Dvoark sets now.