I'm no expert, but at this link are some measurements you'll probably find helpful to answer your questions 1,2 and 3:

http://www.tvantennaplans.com/

4 - If it were me, I'd put it in your attic, not the roof (others here can advise better)
5 - vertical, facing SE
6 - Flat works fine for me, but I've read that some have better reception if the left and right edges of the plate are bend forward a bit (others here can advise better)

Good luck!