What are the requirements of a server to run a Lemmy instance and there is a way to run like a node WO the need to have lots of storage available?

Lemmy uses roughly 150 MB of RAM in the default Docker installation. CPU usage is negligible.

Via: https://join-lemmy.org/docs/en/administration/administration.html.

As for storage that comes down to how many communities you subscribe to, and how active they are.