[s73v3r_]

"You really don't think it's possible that one of the 28 member nations of the EU will pass down an absurdly large fine for some minor infraction?"

For the infraction of having a guestbook? Absolutely not.

"The fact is, if I am not GDPR compliant in any way there is no mechanism built into the law to limit the amount I am fined"

I don't see that as a problem.

" some judge that is in a bad mood or hates the idea of my business can simply fine me 20 million to kill my business and still be abiding by the letter of the law."

Then you appeal. You're acting like there's no recourse or appeals mechanism for you.