What ever you have laying around is a great starting point.

It all comes down to what you want to spend vs what you want to host and how you want to host it.

You could build a raspberry pi docker swarm cluster and get very far. Heck, a single Pi 5 with 4gb of memory will get you on your way. Or you could use an old computer and get just as far. Or you could use a full blown rack mount server with a real IPMI. Or you could use a VPS and accomplish the same thing in the cloud.