HT in large room
For that large open area, you will want efficient 8 ohm floorstanding speakers for the mains.
Check out the Klipsch reference series at a local dealer. If you don't like the horn loaded tweater sound, an Axiom Audio system with M60's, VP150, and QS8's would probably also work well. I think that 5.0 will run around 2-2.5k.
I would consider purchasing a good 12" sub from SVS or HSU ($500-1K) over a Klipsch sub.
For about $700 you can get a Yamaha RX-V2500 or Denon 3805 receiver. That should leave you a little money for speaker wire, cables, DVD player, etc.