I would find a small manufacturer and get a job there, and earn a decent wage while learning the ropes, save my money, and then find a niche to start my own operation. I'd talk to other people in manufacturing and find out what they can't get quickly or consistently enough, and look into what it would take to make that for them and how much margin you can make. I know a boat manufacturer, and he's got a dozen different major components he can no longer reliably get, and so his $800k boats sit unfinished for 6 months at times. Most of these parts are fiberglass or aluminum and don't require a foundry or inaccessibly expensive setups to make (e.g., an aluminum gas tank).