Desktop Style

You can start a small instance with:

CPU: 2
RAM: 4 GB
HD: 40 GB

For Full-text elasticsearch, this increases to:

CPU: 4
RAM: 8 GB

If you switch on relays, you will need extra media storage:
HD: 160 GB

You should also run automated cleanups, otherwise your hard disk will run full.

I am running a single-user instance, so this is a lot lower than what you'll need if you open up registrations. I have:

CPU: 2
RAM: 2 GB
HD: 40 GB