How do you scale your product (servers, databases, support) and which stack do you use?

I'm building a SaaS product that helps organisations collect and streamline feedback and automatically detect frustration signals like rage clicks, form friction etc. Discovering problems fast... before they become big problems. Any Indie founder hopes their startup takes of. But what if it does, how do you scale fast before it all collapses? I will be using MongoDB for fast moving parts and MySQL for user accounts, settings etc. Do you prepare scaling before launch and if yes how do you do that without over preparing? I'm curious about your story!