> Any tips on the minimum hardware or VPS's needed to get a small swarm cluster setup?

From my testing, Docker Swarm is very lightweight, uses less memory than both Hashicorp Nomad and lightweight Kubernetes distros (like K3s). Most of the resource requirements will depend on what containers you actually want to run on the nodes.

You might build a cluster from a bunch of Raspberry Pis, some old OptiPlex boxes or laptops, or whatever you have laying around and it's mostly going to be okay. On a practical level, anything with 1-2 CPU cores and 4 GB of RAM will be okay for running any actually useful software, like a web server/reverse proxy, some databases (PostgreSQL/MySQL/MariaDB), as well as either something for a back end or some pre-packaged software, like Nextcloud.

So, even 5$/month VPSes are more than suitable, even from some of the more cheap hosts like Hetzner or Contabo (though the latter has a bad rep for limited/no support).

That said, you might also want to look at something like Portainer for a nice web based UI, for administering the cluster more easily, it really helps with discoverability and also gives you redeploy web hooks, to make CI easier: https://www.portainer.io/ (works for both Docker Swarm as well as Kubernetes, except the Kubernetes ingress control was a little bit clunky with Traefik instead of Nginx)

You can do Docker Swarm with a single node (both manager and worker). For a high availability setup, you need a majority of manager nodes for a quorum, so a minimum of three nodes to tolerate a single failure.

I actually just migrated my 4-node homelab from Docker Swarm to standalone instances. My nodes all have very different performance characteristics so I had every one of my services restricted to a specific node - in effect, not making use of most of the useful features of Swarm.

Some features of Swarm are nifty, but in particular I found that a) managing every service onto a single node is counter to the point of Swarm and b) I didn't like any of the options for storage. (1. Local storage, making containers even less portable across nodes. 2. Shared replicated storage, complicated. 3. Online file backend, expensive. 4. NFS shares, and then my NAS is a point of failure for every one of my nodes.)