I'm currently at a small startup trying to do ISO 27001. A big issue we run into is that there simply aren't enough people. For example, the processes are built around having one person who writes code, and another person who reviews the written code. That's obviously impossible as a solo dev. You also need an internal auditor, who obviously needs to be separate from the operations team.

If I recall correctly the minimum in a standard setup is 9 roles which cannot overlap. You're going to have a very hard time doing that as a solo entrepreneur, so you'll probably need to find someone who is experienced in making unusual setups like these compliant - which isn't going to be cheap. Even after that there's a pretty decent chance you'll end up needing to hire 3rd-party services in order to be compliant: our "internal" auditor is just some big firm doing it for us.