If you aren't selling user's data, you keep it reasonably secure, and they can delete their account, you are probably good. Most of the services you use will already be GDPR (and Privacy Shield) compliant, and it is easy to list your cloud and payment providers and link to their statements of compliance.
And almost everything a user could ask for, if you don't have an automated solution to, you can generally comply with by checking your email and responding accordingly, so for small userbases, this is hardly really even an issue.
Furthermore, as far as actual enforcement goes, the EU is not going to shut you down or put you out of business on a technicality. They are going to take you out if you show flagrant disregard for your users. This is going to hit the Unroll.me's of the world, not your average web forum.