Start from the assumption that you do not need any data from your users, and do not need to form an explicit relationship with them (like by having them create an account), and work from there. Treat it as a challenge - how to make your idea work under such constraints?

Noted. I'm definitely going to do this for anything else I build.

Thanks for the new perspective.

I think the sign-up is fine, but the password requirements should be done away with. They don't even seem to work. Neither periods or colons count as special symbols. Generally, there shouldn't be any requirements. I use a diceware password, which is very safe, but doesn't fit the requirements.