Well, depending on the size of your bedroom ;) I've seen teams of two people running fairly impressive ML based stuff. They were good enough at it that they didn't remain at two people for very long but that was more than enough to be useful to others. One interesting company - that I'm free to talk about - did a nice one on e-commerce sites to help with risk management: spot fraudulent orders before they ship.

In the long term, and to stay competitive you will always have to get out of bed and go to work. But the initial push can easily be just a very low number of people engaging an otherwise dormant niche.

Yes, medicine has regulatory requirements. But as long as you advise rather than diagnose the regulatory requirements drop to almost nil.