A bank of 3 theater seats is going to be about 8.5' wide, so that leaves for a 2.5' walkway on one side with the other side against the wall. That's pretty tight.

The theater in my last house was 12'2" x 16'6". I did two rows of seating with a sofa and loveseat. They were Ikea Landskrona; the sofa was 80 3/8" wide, and I wouldn't have wanted any wider, but I had walkways on both sides of the sofa.

I would also think about shortening that room. With the length being a multiple of the width, it'll be difficult to get good bass response. This isn't about being loud, but rather some frequencies could sound 'boomy' and others just disappear.

Check out the dedicated home theater subform over on avsforum.com. Lots of helpful DIY'ers and pros there. Also lots of inspiration.

3-row arm chair seating is 94" you will have 3'2" walkway passage

3-seat sofa is 80" you will have more room.

Keep in mind if you plan on using a tier platform for your seating it will reduce the walkway area by at least 6-8" so sofa would probably work best.

Here is an image of some configurations should give you a rough planning start, of course it will also depends who and where you buy and what the spec dimensions they will have.

This is from Home Theater Interiors products.