Depends on how many communities do you subscribe too and how much activity they have.
I'm running my single user instance subscribed to 20 communities on a 2c/4g vps who also hosts my matrix server and a bunch of other stuff and right now I mostly see peaks from 5/10% of CPU and RAM at 1.5GB
I have been running for 15months and the docker volumes total 1.2GBs A single pg_dump for the lemmy database in plain text is 450M
For the whole stack in the past 16 hours
# docker-compose stats