Of course the first thing I did was check your profile to see if you were close to me!

A search at www.cedia.net (then click on "find a designer")will give you quite a few local contractors to choose from. While we would all like to be the only one... interview a few. Establish a budget and be ready to have it squashed as you find all of the aspects that you never even thought of adding thousands of dollars to your project. Eventually, as AVGenius said, pick one and make your involvement with him/her worth the time spent (please realize that professionals need to be profitable and don't string them along for knowledge)... even if your budget constrains you from having him/her do the whole project.

As far as a projector... since you are looking for recommendations... the Dwin Transvision 3+. I know the price will scare you but my company has sold these to many people looking at a 3K prjector and had them happy about it in the end. With an outboard native resolution scaler that connects to all of your video sources you need to run just one DVI-D cable to the projector... as technologies change you will be able to reconfigure things at the head end without having to rip sheetrock to run new cables to the projector. Give it a serious look.

As far as screen size... assuming you are sitting about 12-13 feet away and that your screen will be on the 11' wall. I would personally max out about a 96" diagonal screen. Anything bigger makes it too hard to take it all in. The formula for 4:3 ratios was to take the seating area distance in inches and divide in half. (13' = 156" divided by two = 78"). I derive the 16:9 equivalent by dividing this # by three and multiplying it by 4. I then go a few inches down as thats my personal comfort (that formula brings up a 104" screen)

Good luck in your project!