So about one per second (up to ten, less conservatively). I concur. But if you think your site might ever scale beyond that, do yourself a favor and use Postgres from the get-go.
The vast, vast majority of websites never see anything even close to that, so it's a safe bet unless you have some specific reason to expect it to reach that kind of traffic, or you are dealing with workloads that SQLite really does not handle well, e.g. many concurrent writes. And if your workload is mostly reads, then you probably can use a cache layer, which allows SQLite to go further still.
Adding a cache layer to keep using the wrong database is an architecture failure - if you use Postgres from the get go you will not need the cache until way way later on anyway. (Side note, I’m team MySql but the same point applies)