Hello again - I read that there is also a systemdb - does this need to be project-specific or can I reuse one PostgreSQL database for all meltano projects ?

You can use the same database. I'd recommend either using a

--state-id-suffix

if to identify runs from different projects and allow concurrent runs, or using separate schemas for each project: https://docs.meltano.com/reference/settings/#targeting-a-postgresql-schema

Perfect thanks a lot