I don't use any GUI... I use terraform in the terminal or via CI/CD. There is an API and also a Terraform provider for Proxmox, and I can use that, together with Ansible and shell scripts to manage VMs, but I was looking for k8s support.
Again, it works fine for small environments, with a bit of manual work and human intervention, but for larger ones, I need a bit more. I moved away from a few VMs acting as k8s nodes, to k8s as a service (at work).
you can get away with half that. i run my setup (similar to what you wrote) on a dell micro sff with an i5 6500t and 16gb ram that i paid 90€ for. not the snappiest, but works just fine.