First off, have a look through this http://www.dtvforum.info/index.php?showtopic=31244
1. Not sure, but i would break the budget down into; AVR $1500, Fronts $2000, Sub $1000, Centre $500, Rears $500, Player $500. (Total $6k) Or thereabouts.
2. If you game a fair bit, have you considered a ps3?
3. Cabling, if you need everything ~$250 dependant on lenght and quality.
4. http://www.dtvforum.info/index.php?showtopic=40757
5. Buy an SPL meter and do it yourself.
6. IMO Planet Earth
7. You can if you want, the speakers are inserted and removed from the front so why not make it removable.