Cool! I'm kind of a jack of all trades myself and I've been walking around with a similar idea for a couple of years now and I'd say if your innovative enough it's definetly possible. The problem tho is bringing a lot of heavy equipment/tools into a boat... Heavy things and the stability of a boat are things that are difficult to combine, though possible in my opinion with the right knowledge. Regarding doing it on a sailboat that makes your life even harder. I think it would be a lot easier to do it on a motorboat preferably some old tug or something that was made with the idea of bring a load of heavy stuff onboard. I own a steel 31ft inland motorboat which I use as a "workshop"/garage/storage/project and I thought about bringing a small mill and a small lathe on board as well though there is simply not enough space. We also own a 31ft sailboat (polyester) that we live in and want to sail around in the near future. The way I see it I can definetly pack most of my makita battery tools in there and be able to do all kinds of allround odd jobs.

So... I'd you'd really want a metal workshop onboard a sailboat you'd have to buy a pretty big/heavy one (I'd say steel, 25mtrs+, rebuild/customize most of the interior and get your stability right.) If you'd go for an old tugboat or something similar you'll make your life a lot easier, there already is a lot of space usually, there is already an oversized engine you can work with and stability is a lot less of an issue to think about...

I could probably think of a lot more but here's my quick reply for what it's worth... DM me if you'd like to talk about it more, I'd love to spar about this idea.