1. If you've got room for tower speakers vs small satellites by all means go with the tower speakers.
2. yes, big difference as the towers do a much better job of filling up the room than sats.
3. Depends on your budget. If you can afford the Polk system then it would be most cost effective.
4. Any entry/mid level Denon, Onkyo, Yamaha, Pioneer AV receiver that has some type of room correction
5. I would get towers over sats every time.
6. Pioneer Andre Jones speakers, Infinity P363 towers, Fry's sells some JBL towers also..
7. yes, you could use the Energy sats as surrounds but I'd probably want a larger sub than the 8" Energy sub. The Energy center will not work with the Polk towers, you need to buy a Polk center.
You never did mention the size of your room. What are the dimensions?