I'm running 1 vCPU, 2GB of RAM and 25GB of disk at the moment for my tiny instance (we have like 5 users?). I started with 1GB of RAM but it quickly started swapping on disk and causing performance issues. I should probably bring it up to 4GB but it's not necessary yet so I'm delaying.
Something I'd like to implement is object storage for pictures (via AWS S3 bucket) as detailed here: https://lemmy.eus/comment/164368