If it’s relevant to your actual job, learning to use k8s will benefit you more. Generally i’d prefer to keep the bare metal OS as clean as possible to avoid breaking anything during upgrades and such, and keep the containers and normal running apps on separate VMs that can communicate with eachothers, k8s is mostly good if you got a lot of servers and want to manage them all at once through a single “orchestrator”. But for self hosting stuff in your home it’s kinda overkill. But it still can be used to manage things up. So imo go for k8s since it can be used in homeservers, it’s just that it’s kinda like using a nuclear bomb to kill a wasp.
Just stick to signal, matrix can be used the same way but it’s a lot more complicated and requires involvement in keeping your backup key safe, otherwise you’ll lose every encrypted message! Signal is similar to whatsapp. (which is obviously…a popular app…which should already explain the simplicity of setting it up.)