Once you have laid out the theater room and seen what space you have available, you can determine what home theater seating options are appropriate.  Given the space remaining, how many chairs or couches are realistic?  Make sure to take into account whether you will want side tables or a coffee table in the room.  True theater style chairs give you the most seating for the space but they may not be the most comfortable.  More comfortable chairs tend to be wider and plusher which takes up more floor space.  If you have kids, you may want to consider seats with cup holders in them to both save space and protect against spills.  Otherwise, coffee tables will definitely be needed.

Talk to a local home theater system retailer about home theater seating options. They usually have great lines into the manufactures that specifically cater to home theater design.