What are my qualifications for giving advice on this subject?
I have been a contractor for a long time. I am a one-man-band, self-promoter, entrepreneur. I could have had my own company but I have chosen to work through agencies. I find my own jobs, so they don't get a big cut but I have a lot less paperwork. I do not like to work too hard.
I have investigated franchises and other businesses that I could start and nothing ever measured up. I can make too much working in my industry, and there is no upper age limit for contractors.
When I hang up the slide rule, I can go on the road as an instructor in various technologies of my acquaintance that happen to be in demand right now (but maybe not after I retire).
In any case, I plan to start a small testing lab in cahoots with an old bud who is an expert in his field. We are building it a bit at a time for low cost. With luck, I will make enough to pay for my gas driving to and from the shop. If absolutely necessary, I can employ DS to be the tech. All for fun. If I seriously needed to have a paying business to survive, I might do something else.
If I really have to, I can find or make a job of some kind. Working for one's-self is REALLY hard work. If I wanted to work that hard, I would have done it long ago and be rich and long gone by now.