Next up is the plexiglass. Luckily, I've already found that this site has some tutorials on using plexiglass, but I just wanted to clarify a few things, primarily this: how much bigger than the 'hole' should the plexiglass be cut?
Well that depends on the type of installation you're planning to use. If you are going to use something like the H-Lock window trim then this
will help. If you're planning on mounting the window with double sided tape, silicone, or similar adheasive, then you will want to give yourself roughly 3/8 - 1/2 around the window opening to do so. If you're planning on bolting the window in, then I would do a test piece to see how well the plexi that you use handles the stress of the bolt hole and bolt install. Sometimes if you don't leave enough room on the edge it will crack from drilling it or even bolting it.
Thirdly, can the same process that is used for modding PC's be used to mod, say, XBoxes?