This is like so many other things with a seastead as it requires foresight and tact.
I see no problem having a medical seastead that is accepted by the international community and is seastead based without sponsorship of a particular country. There are already ship based examples out there.
First you will need credibility and that will only come with self made standards above what is expected from the public at large. Your doctors will need credentials and you’ll need to insure quality care.
Second, if you start with generally accepted care and build a reputation, it will be much easier for more controversial treatments later.
Third, you’ll need to show a track record for treatments that are outside those of your neighbors. If you can show results, it is much harder for an outside entity to try to fight you on it.
As far as equipment goes, yes it is expensive, but the income opportunities are just as great. A medical seastead will need deep pockets but gives a big reward to investors. Government is not needed on this front.