Here are a few thoughts:
Be sure that you scope out the market very carefully. Be sure that you know where the money is found: Who pays how much for what? What can I make? What are the risks? What is the cost of my insurance? Will I enjoy this?
Don't be fooled into thinking that what you love or like to do is what pays well. One thing that I really enjoy doing is small circuit design. Unfortunately, that is a cut-throat business that I only engage in on rare occasion. The real money is often found in rather mundane jobs with the really cool stuff less common - like icing on a cake.
I should say that I have noticed quite a few niche markets in the after-market, high performance auto industry. After-market products for cars generally can also be good. I knew a guy who paid his way through college by selling a fake burglar alarm for cars. It was just a flashing LED that was mounted in the dash to look like the LED from an alarm. He sold it locally in auto and hardware stores.
Finally, since going out on my own six years ago, when I am really busy, my average work week is 80-100 Hrs or more. It has been as high as 110 hours I think. As a rule I can bill about half of that time as profit. That is considered a very good average. On the up side, after a good run I have taken up to two months off [mostly] at a time. The freedom is wonderful!
There is nothing like calling your own shots. I don’t know if I could work for someone else any longer. The sense of autonomy is absolutely addictive for me. Also, when the economy went south, I found that due to my base of customers I was able to squeak by while other’s in my field lost their jobs and sometimes had to relocate. I have found that in some ways I am more secure being self employed than if I was an employee. When you work for someone else all of your eggs are in one basket; so to speak. This is like me only having one customer; which if preventable, I would never, never allow to happen. So, in a strange way, working for someone else as an employee is like a bad business practice.
My motto: Success is 1% inspiration and 99% perspiration. - Thomas Edison.
Good luck.