Basically, have legal entity, legally maintain it, don’t be negligent, don’t commit fraud, and have legally enforceable termination clause in your contracts.
My core point was don’t ask for legal advice on the internet; have lots of legal experience and given the simplicity of your question, to me it tells me that you don’t either have the desire to do your own research and/or experience to do it; which is fine, but lots of people on the internet will claim they know what they’re saying and frequently do not or don’t have time to understand specifics of your situation.
All and all, to me, sounds like you under estimating how hard it is to sell people; that is, even if you had a legal and literally copy of the software and knew how to operate it at the scale needed, why would those companies do business with you?
(Please don’t answer, just trying to make the point that business is not just about having a solution people need.)