how do I cut the square windows?
can't you see? "badly". that's how. ha! 
the black plastic cuts just by looking at it, so its not hard. its soft plastic that you can use a nibbling tool (once you drill a round hole large enough to start with) and just nibble until you are close enough. then its file tool or maybe xacto knife if you need to cut bigger chunks.
for metal, its just a lot of work if using hand tools (me) and so I avoid it. one chassis was metal but I try to use this non-splinter non-cracking plastic stuff at my plastic store (TAP). the crinkle finish helps hide a lot of 'hardware overruns' (lol) too.