For EGw min:
2 CPU
2 GB RAM
I run an installation for (during the day) ~90 users with 4 CPU and 6GB RAM. That’s about twice what it need.
This then runs lean on a Debian. With the installation, I still supply employees in the home office with Guacamole.
I once wrote something about it:
https://help.egroupware.org/t/installation-egroupware-auf-ionos-vserver-vps/76890
The database remains very small because no binary data is stored in it. In the above installation, the EGroupware database dump is just 22MB in size. After 14 years without deletion…
What you need The space for files in the file manager, attachments of tasks, contacts, … you have to calculate yourself.
But as always:
You have to watch that. In principle, EGw is quite resource-efficient.
Stefan