> 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.

No, you couldn't, and no, you wouldn't.

To build a swarm you need a lot of fiddling and tooling. Where are you keeping them? How are they all connected? What's the clustering software? How is this any better than an old PC with a few SSDs?

Raspberry Pi with any amount of RAM is an exercise in frustration: it's abysmally slow for any kind of work or experimentation.

Really, the only useful advice is to use an old PC or use a VPS or a dedicated server somewhere.