I'm a hands on guy also and worked my butt off as a Field I/T Tech to work up to a better paying desk job which I hated.
Now I'm back in the field with less pay, but back on OT pay and much happier. Desk/office jobs are way over-rated IMO.
As for side income, I've found that selling anything is a tough way to make any money. But providing services with a skill that you have is much easier.
I was flipping used cars, only Honda's. Find a decent deal, fix them up (simple and cosmetic stuff) made a few dollars but wasn't worth it to keep the cars around the driveway, etc.
So then I was doing small automotive jobs for friends, neighbours, co-workers, Honda & Mustang guys.. No real money in that..
But then I bought a Dodge diesel and started learning and modding my own truck. This was 8 years ago. Taught myself everything possible about diesels and these trucks. Discovered that there is a huge demand for Dodge Cummins light truck repair and performance upgrades.
The light truck diesel market is the fastest growing performance segment.
All other performance segments, imports, muscle cars, restoration, etc, are in decline.
There is a ton of these trucks sold every year, and this market has money unlike the young Honda/Import and Mustang market.
I have a fully equipped garage with a ton of tools that I've collected over the years. I've been wrenching, welding and rodding since I was 10 years old. Now over 40!!
Some of the jobs can go into the tank and you'll lose time, not necessarily money, on them. I stick with simple upgrades and repairs. Pulling a 400 lb transmission and transfer case is no fun but electronic repairs can be frustrating.
I find upgrades to be easiest and most profitable. All cash money, no taxes..
So I would recommend trying to provide automotive, a/c or carpentry services, etc, rather than trying to sell products.
Just my thoughts, I hope this info is useful...