I think stitch count is an embroidery machine thing? I can easily put 300K to 600K stitches on a single quilt, depending on size of quilt and density of stitches. I know a few show quilters who can put over a million stitches on one quilt.
When I was shopping longarms, the first thing I did was check around with all my longarm quilting friends (about 20 of us) to see what they had and what they liked/disliked. Most of them, over several years, moved from various brands (Nolting, APQS, Voyager, A1, etc) to one single brand (Innova) and were very happy. (We are all now Innova owners with 2 holdouts - one Gammill and one HQ.)
The next thing I did was take a 5-hour class that was designed to teach you how to use the longarm in preparation for renting time on it. The instructor had us doing EVERYTHING on it, from winding bobbins, loading the quilt onto the frame, adjusting tension, troubleshooting, to actually quilting, FMQ, how to use rulers, and she gave us little quilting assignments that essentially had us putting the sew head through its paces. The only thing I didn't play with was robotics because I already knew I wasn't interested in them.
Once I decided on a brand, I shopped all the used market machines. My dealer is amazing - I'd see a machine for sale somewhere and call him up to ask him about it. He could tell me how old that machine was, when the machine was last serviced, if it had had any past issues, if the owner used it for hobby quilting or was a professional, etc. I remember calling him about one advertised on Craig's List. He looked at the picture on the listing and told me it had been purchased by a quilter who had unexpectedly passed about a year after purchase, so the husband donated it to their church. It had been used to quilt maybe 10 quilts before the church decided to sell it.
So in short, I guess my advice is to take a class that gives you at least an hour to putter on the longarm, make friends with your dealer, tell them what you're looking for (and be patient for it). And go to all your quilting friends houses and look at their setups. Ask them what they like the best about their longarm and what they would change or do differently if they could. I think the most common "regret" I've heard is getting too small of a machine head, frame, or both. It's better to have it and not need it, than need it and not have it.
My husband actually bought a new Innova for me for Christmas. He consulted my closest quilting friend to ask what he should and shouldn't get as far as specs and accessories go, and if she didn't know the answer, she was very good at sneakily asking me the question without giving me any hints. So I ended up with a light bar, hydraulic lift, and a 26" sew head. I didn't think I'd use the hydraulic lift much, boy was I wrong.