You probably don't need Redis until you have thousands of requests per minute, nevermind per day.

I'd go further and even say per second! Actually PG can still handle it, the main problem is that it has a more complex runtime that can spike. Backups? Background jobs doing heavy writes? Replication? Vacuum? Can tend to cause multisecond slowdowns which may be undesirable depending on your SLA. But otherwise it would be fine.