Arch because my installs keep working, and I'm really used to it at this point. In the future I'd be interested in trying something like NixOS/Guix, Silverblue, or Qubes.
The mobile landscape is just a privacy clusterfuck. I flip flop back and forth between Android and iOS a lot. Maybe one day I'll take the Graphene plunge, not sure.
It's very gracious of you to stand up this instance with your own resources. I'm used to the idea of donating to my fedi home instances, and other fediverse regulars are probably the same way. Just give us the word if you do need donations down the road (ie. for storage upgrades, etc).