Paper Princess is right on the target on this subject. I would also add that it would be smart to take a lesson and rent time on a long arm at a local shop(most require you take the class to be able to rent time). A long arm (or even a mid-arm or a sit-down) is very costly and you should make sure that you like quilting first. I have a friend who's DH bought her a long arm (APQS) and she HATES the quilting process--loves to piece! So now he uses it for charity quilts.
When I was looking, I think it was Long Arm University website that had some excellent checklists for potential long arm owners to think about.