From a scalability perspective, the number of users isn’t actually very relevant. That’s why Bubble doesn’t really charge “per user”. The potential areas for failure for web apps are usually some of the following (not exclusive to Bubble apps):
- Your app requires making many requests to the same server simultaneously
- Your app requires processing of a lot of very heavy data/files
- Your app requires having many users connected to the same real-time database (Bubble doesn’t have a real-time database so you’re safe there).
If your app doesn’t require constant back-and-forth between your users and the Bubble server, I think you’re safe. You could have millions of users without an issue. A typical web app with REST APIs is a lot less resource-intensive than most people imagine.