Ask HN: What should I prepare to run a business that sells customer's data?

Hear me out, to make it simple, I think that... selling software is not profitable enough for my current market (third world country). This market seems okay to pick the free alternative (ex: it's fine to use google analytic, compared to paid one like simple analytic or fathom analytic). What should I prepare in terms of like legal, or anything that's not mentioned here? Since, I'll need to enable the (here we go) "Freemium model" and ads based revenue.