It sounds like you are well on your way to being a long arm quilter.! Good for you!!
Most people I know who bought long arms and were convinced by the sales people that they too could quilt for others found they don't enjoy the experience. That it took them 2-5 years to feel comfortable doing things for others. That people are picky picky picky (and justifiably so) and cheap. That the tops are not necessarily really ready for machine quilting for a variety of reasons. The reasons go on and on, but typically more involve the people than the quilts...
I think that since you are already thinking of sales and have pieces you are ready and willing to sell, you are ahead of the curve. The successful long armers I know are typically kept busy by word of mouth or just a card on the bulletin board at the local quilt store. If you have a quilt guild in the area that has a service project (Quilts of Valor, Project Linus, etc) you might volunteer to quilt down some of the projects in exchange for feedback/exposure -- be clear and firm on how many you are willing to do.
I recently bought a used long arm system, been getting some organizational stuff at home out of the way before I set it up. Need to order some storage for other things and move some furniture around and it will be easy with the large empty space. I am very clear that I do not want to quilt for other people, I'd be happy to let the ladies in my sewing group come visit and do it themselves. Once I get through my backlog of tops, a couple of years from now I might be willing to quilt down a few donation quilts.