I have been long arming for not quite 2 years and think I just completed my 40th quilt. One of the first questions I was asked when guild members heard of my purchase was, "Are you going to quilt for others?" I said "no", I was doing this for myself. A good deal on a used machine from a reputable source was too good for me to pass up. I can meander on my plain Jane machine and have expanded out to pantographs. At this time my meandering skills are saleable, but my panto skills are not!
The responses listed have very valid points. I would like to add the question: is your time flexible enough to accommodate customer deadlines? Also, a great deal depends on what kind of machine you purchase (good for you for doing your homework). Will it be strictly FMQ/pantographs or have computer aided capabilities? There is a learning curve in setting up the computer programs as well. I work in a LQS that offers quilting services and I witnessed the time it took the operator (an experienced LA'er) to get the machine to do what she wanted.
Demand for quilting services depend on how many quilters are in your area and how many LA'ers there are...simply put supply and demand. At the LQS, right now turn around time is about a month. And in our rural community I know of 3 other independent for hire LA'ers in a 15 mile radius.
Best of luck in your decision with the purchase of your machine. You are asking the right questions.