I will, but I need to work up a new, beefier model first.
You can use the cutting wheel, yes. If you've got a firm, steady grip, I'd recommend a tile cutting bit or a spiral saw bit. They have a tendency to walk a bit if you don't hold on tightly and cut slow, but you can get closer to the corners before you have to fine-tune the edges with sanding drums and files.
I'd hold off on painting the inside until you're done with all of the cutting. The middle layers of resin are tinted as close as I could get them to the gold of the helmet, but you'll still probably want to black them out when all is said and done.
Once you get everything all done, be sure to post pictures of the finished product. I love seeing these all put together.
If anybody else want to get in on this run, please post here and I'll PM you with the details.