Polk RM6750 and Monitor-50 questions

[Bassman]

I am in the process of remodeling my basement and half of it will be a home theater. The space will be 11 x 24 feet. The TV will be on one end and the main seating will be about 14 to 15 feet back. This will be a set of recliners. There may be additional seating along the walls. There will be about 8 to 10 feet behind the seating. I am not sure what will be back there yet.

I have been buying audio components when I find them on sale. This is what I have so far.
Sony STR-DG820 7.1: $199
(http://www.sonystyle.com/webapp/wcs/...52921665364791 )

Polk Audio RM6750 5.1 home theater speaker system: $199
( http://www.polkaudio.com/homeaudio/products/rm6750 )

When the room is completed I plan to buy a Sony 52 inch XBR-6 and a Sony Blue Ray player.

I have two questions on the audio system.

1- Is the RM6750 5.1 good enough for this size room? I will be using two of the RM6750 speakers for the front speaker.
2- I may add two new speakers for the front speaker and use the RM6750 speakers for the surround and rear speakers to make a 7.1 system. The speakers that I am looking at are the Polk Audio Monitor 50's ($99 each). Will the Monitor 50's match up with the RM6750 system? The RM6750 system came with 4 satellite speakers, center speaker and sub-woofer.

3- If I go with the 7.1 system, where should the surround speakers be placed for this shape of room?

Thanks for your help!