Hi and welcome!!
1. No, that green inner lining does not stain
2. Macbook speakers suck really bad. Voice/video chats are near inaudible in a normal activity environment.
3. The screen is awesome. I lived on it for 6 months in different settings and never had a problem. Outdoors/indoors
4. Yes, networking between a Mac and a PC is awesome. My wife has an old beat up Japanese Windows OS laptop, and it networks with everything fine.
5. Gaming on the Macbook is near non-existent. If you want to do the minimal gaming that it "may" be capable of, despite what parallels says, it isn't enough. Boot camp is the best route, but if you have to buy an OS, I would just scrap that plan.
These are not the best answers, but they are the answers that I wish someone had given me prior to purchasing my Macbook. I recently upgraded to a Macbook pro. You will eventually want to do that. The Macbook is a sweet machine though.