I'm currently saving up to buy a fractal design node 804 to build a NAS with 4 drives within. Also trying to create some more reliable backups using said NAS.
From my experience, Cities Skylines works great through proton on steam (it's a compatibility layer for windows games) and Minecraft has it's own native launcher (which is downloadable from their site here, you need to use the debian installer for ubuntu). As far as ubuntu native, I haven't used it a lot. Linux mint is a distro recommended for people who are used to windows most often, you can take a look around.
As far as the other games go, only slime rancher is one that I know doesn't work through steam. For most games you can take a look at protondb, where you can just search for the game.
Okay, I'll start with configuring pihole for DNS. If I get it, I can just use that DNS and if I need to access a service external I need to register the domain with my registrar?
You can get more updated packages by running debian testing, which is quite stable. Debian also is more stable. Security patches are still brought to the main release, making it secure. The stability comes from the lack of a lot of new updates which come with a lot of new bugs.
pterodactyl looks really neat, will definitely look into that. I have a manual system for my media library, so I want to add the directories with artwork and movies manually to the directory which jellyfin reads.
I use the names of greek deities for my host names, mostly geared towards the function of the server/computer.