Answers
The holders of a residence permit without access to employment, who fall under the regulations of the immigration law, must have a private insurance, for themselves and their family members, that covers their healthcare and medical care expenses. The insurance obligation is a prerequisite for the residence permit issuance as well. Such kind of contracts available in Greece are not expensive in general.
The golden visa applicant has no health or social insurance rights.
It depends on the way the applicant establishes themselves in Greece. If you do not work here and come as an investor etc., you would need to pay private insurance, which generally is not
very expensive in Greece.