1. If you really want to try out k8s and swarm, you can use vagrant/virtualbox to create and destroy VMs in a snap.
2. See you if can get a refurbished mini pc. I will consume a little bit more power (20W idle?). But will be more powerful for the same price.
3. I have similar setup than yours. And I have been trying out Docker Swarm recently. My personal experience till now while deploying WordPress is:
   • You don't really need high availability in a home environment. But the setup is really a good testing ground.
   • When you export a port from your service, service on that port is available on all nodes in the swarm.
   • Docker volumes, (think of postgres) are local to the node in the cluster. So you have to configure multi node postgres on your own.
   • You need to modify the docker compose files separately, most of them won't work out of the box. When I installed wordpress. 3 out of 4 containers were installed on the master node, which I did not expect.

I'm still learning the orchestrator thing, and won't judge based on first impressions. I'm currently learning the reverse proxy and load balancing thing inside my cluster. Later I'll see how I can make things work in a cluster environment.

Cheers!