Couple thousand simultaneous should be fine, depending on total system load, whether you're running on spinning disks or on SSDs, p50/99 latency demands and of course you'd need to enable the WAL pragma to allow simultaneous writes in the first place. Run an experiment to be sure about your specific situation.

You also need BEGIN CONCURRENT to allow simultaneous write transactions.

https://www.sqlite.org/src/doc/begin-concurrent/doc/begin_co...