Mhlayne - I would like to offer a small suggestion, based on my own recent FIRST TIME experiences with a helmet: Don't cut the key slots out yet; wait until all of your sanding and polishing is complete. In fact, if there is a way for you to hot glue the visor piece that you cut out back in, it would offer some more stability while you're sanding, which equals less chance of small hairline cracks due to torquing of the cheeks while you're sanding. I was so excited to cut things out so it looked more like a Fett helmet that I had (and still am) to deal with some small hairline cracks. Other than that it looks great. When the time comes to install the key slots here is what I did (which is by no means THE best way; it just worked for me):
1. Be sure to polish the key slots the same as you do the helmet
2. Cut out the opening on the helmet
3. Place the keyslots inside the helmet and trace the cut out area of the helmet onto the key slots (did that make sense?)
4. Use your dremmel to cut the traced lines, leaving just a tad-bit of excess
5. Hand file, try to install, hand file, try to install, hand file, try to....you get the idea.
6. Once it is installed, glue, epoxy, whatever you choose to keep it in place. Hot glue the mesh in place.
7. Weather the seams to hide any unsavory work
I'm pretty sure there are different, better, easier, etc. methods, but this is one. Good luck!
Jason