Do you want a development install or a production install? If it’s the latter, then seeDiscourse official Standard Installation. Running under k8s is possible, but it’s not straightforward, as you need to use ./launcher to build the container. And doing a full no-downtime upgrade requires a few steps that are not immediately obvious. If you want it to be easy, just spin up a VM (a bit easier if it runs Ubuntu or Debian).
Yes, you need to be able to send email for production. For development, you obviously don’t need that.