If I were to do this all over again, I don't think I would do it this way at all. I would use something like Caddy which manages it's own config and has an API

If I were to do this all over again, I don't think I would do it this way at all. I would use something like Caddy which manages it's own config and has an API for live updates. SQLite for the user management and administration. I would possibly have 2 Caddy nodes though, with a LB between them (instead of my potentially flawed heartbeat floating IP mechanism). The application would do an atomic update to both Caddy servers, if either failed, it would roll it back. But you are still looking at around $30-40/mo for hosting, not saving much money, but making it much simpler and saving headaches.