I set those using the Sustem Settings (KDE) and Tweaks (GNOME). To me all fonts look a bit different between Gnome and KDE.
1.It doesn't support DoH 2.It's set per connection, not system-wide. If you connect to another wifi network you have to set dns again.
Here you go: https://github.com/Start9Labs/start-os https://gitlab.com/hsleisink/orb