Adding to this (which is a solid recommendation and answer BTW), you can try out podman kube play <your-file>.yaml (see here) before going full k8s or k3s setup to familiarize yourself with the concepts, without moving too far away from the docker-compose ease of use.

Regarding question 1, any distro works, but if your are looking specifically for a lightweight, fast to deploy node host os, I recommend opensuse microOS/leap micro or similarly, fedora coreOS. With both you can drop a combustion/butane/ignition config file in a usb installer partition, so you can quickly integrate fresh installs in your cluster (ssh, network config, user accounts, package installs) see https://opensuse.github.io/fuel-ignition/

… U, V, W comes before X, Y, Z

If coming first is an advantage or not… well

(☞ ͡° ͜ʖ ͡°)☞