What country do you live in? As far as I know, there are no schools in the US where you can get trained/certified in Rife therapy since it is still technically outlawed by the FDA. The reason that the Spooky units can be sold legally is because the company does not make any specific claims that the hardware or software can "cure" any disease or illness. It's mostly user-based and still considered "experimental". There are schools in the UK and eastern Europe that offer training in alternative health that include Rife but I do not know if there are specific degree programs.
As for liability insurance, that's also going to be an issue, again because the FDA has strictly limited what services are "legal" and "illegal" and what claims can be made. The organization I linked below used to be my carrier when I started doing PEMF and Far-Infrared therapy but after a couple years, I decided I did not need it so dropped my coverage. I was one of the only people at that time they were covering who was providing these services but I can only assume they have more now since PEMF therapy has been gaining in popularity. You could try checking with them.
I think as long as you have a good liability waiver form that is signed by your clients and it clearly states that you are not "diagnosing, treating, or curing any illness, disease, or condition", you will be fine. Just be careful about what claims you make and be upfront with the people you are working with about expectations.