Heya Mr. Moholic,
I started to answer your question but remembered This excellent article on 5.1 and 7.1 layouts. It is a great article from resident audio expert Alan Loft and it has very well done diagrams showing the optimum layouts for both 5.1 and 7.1, direct radiating vs. di and quad-polar speakers, and even sub woofer locations. It also talks about how optimum is not always a possible reality so you do what you can with what you have.

I think it will answer a lot of your questions. It did for me a t the time.

With great power comes Awesome irresponsibility.