My useless advice: Do it in phases as you learn.

• Start off with Yunohost. It is simple to get started and works pretty well. Try different apps to see what you like and what might be worth using for real. Just make sure that you keep in mind this is more of a “proof of concept” for testing things. Unless you plan to purchase another mini pc later.
• When you feel like you have out grown it and want to start learning more about things, you can move to something like Proxmox. This allows you to create virtual machines and play with containers (docker/lxc). If you plan well, you can back up your Yunohost data and configs to another drive, wipe Yunohost install and replace it with Proxmox. Then install a VM running Yunohost and restore your data and configs you previously backed up.
• Then you can start playing with lxc containers and docker containers.
• If you can get a second machine with multiple drives, install TrueNAS or OMV. Use that to store all of your data on NFS drive that you mount from your Proxmox VMs and containers.

Years ago I used to run a linux server with everything installed under Apache virtual directories and fought the constant upgrade cycle. Life got in the way and I gave up on it until the pandemic slowed life down enough for me to start playing again. So I went the Yunhost route on an old Mac Mini. I now have a 3 node Proxmox cluster with Yunhost in a VM (with a dozen apps running on it) and another 15-20 containers running under either lxc or docker. I eventually purchased a cheap NAS device for data storage so that I could make use of the Proxmox fail over capabilities.

If your mini pc has the capability for two drives, install the OS on one and store data on the other (unless/until you get a second pc/NAS).

Linux for sure. Whatever distro seems cool to you.