1. Use whatever you already know.
2. Start building now.
It’s okay not to write unit tests at the beginning.
It’s okay to run everything on a single ec2 instance.
It’s okay to not have “forgot password” flow when you launch your project v0.1.
It’s okay to ssh into server to deploy code at the beginning.
Many billion-dollar companies were using pretty bad software engineering practices at the beginning of their life (maybe first 5 years). Engineering is just a small part of a tech business.