Per https://community.torproject.org/relay/relays-requirements/

A <40 Mbit/s non-exit relay should have at least 512 MB of RAM available.
A non-exit relay faster than 40 Mbit/s should have at least 1 GB of RAM.
On an exit relay we recommend at least 1.5 GB of RAM per tor instance.

Not sure about the control panel to manage it, but that'd add overhead to the RAM requirement. Hopefully someone will correct me if I'm wrong, but I'm pretty sure it's "set it and forget it". What are you wanting to do with a control panel? See network graphs and stats and stuff? Observium or Librenms will collect pretty much any server related stat that you could ever need. Those will chart and graph things like CPU, RAM, Disk IO, Network Graphs, uptime, etc all over time. From very recent to multiple years if you keep it running long enough.