Comment by rtp4me

For 4) - consider PGHero[1] and PGTuner[2] instead of a full-time DBA. We use both in production and they work very well to help track down performance issues with Postgres.

[1] https://github.com/ankane/pghero

[2] https://pgtune.leopard.in.ua/

Edit: For the record, I have worked at a few small companies as the "SysAdmin" guy who did the whole compliment of servers, OS, storage, networking, VMs, DB, perf tuning, etc.