I've run a small business for 34 years (very small now) and also worked for a wage at times simultaneously. I started out as a craftsman renting shop space producing high quality wooden boats and quickly learned that it was barely possible to survive that way. Many of the supposed "business" requirements dropped by the wayside -- business checking accounts, business phone, renting space, etc.
I'm in total agreement with what John Stevenson has said. The simpler and least "business like" you can make it, starting out, the better.
Just make a product, a single item, and sell it. Don't spend anything on anything. When it sells you will have a feel for what your time and materials will be and what the market will be. You can improve on both of those over time, since it's a one-off, and you are an unknown in the market, and you expect to change both of those, but your expenses will also increase over time.
You will likely find that the reduction in costs even when doing multiples and jigging, as well as an increase in the selling price by becoming better known, isn't dramatic, because you start to have to become more of a business, unless you have very good luck and some kind of unanticipated advantage -- like a famous band using your instruments.
The real problem is likely to be that what you love isn't being a business man, it is making things. Yet to become reasonably self supporting you may need to like being a business man, and spend more time doing that than making things.
I'm not saying it's impossible, I'm just saying it's hard, and usually not as much fun as you expect.
One other really crucial piece of advice, and that is:
Information is much more marketable, and profitable, than real goods. If you know how to make something that is difficult, and to which you bring unique insights and talents, that can be your real product. People will buy information on how you build your instruments, if what you present is unique, truthful, well done, and interesting.
You already have a start on that with your interesting, and high quality videos. Don't ignore that aspect of what you like to do.