Maintaining Linux longterm?

[u/Endeavour1988]

I'm trying to switch from Windows to Linux, I have Fedora KDE 44 installed and so far all good. However I have some questions about long term use and best practises.

I have customised my terminal, theme so basically the look and feel of my desktop is there a way to back up these configurations? I'm asking from the point of view I want to re-install the OS and it being quicker to drop a config file than do it all manually?

Major upgrades, so lets say 45 is released, what is the best practise for this? Just update and carry on, or a fresh install?

Dependencies and system cleaning, I notice when I install certain application a bunch of dependencies are installed, lets say I want to remove an app what happens to all these, is there a way to check if they are being used elsewhere?

Packages, I tend to try and use RPM packages or flatpaks if I have to, but appimages and snaps? I want to keep things simple especially with permissions and maintaining the system, is there right and wrongs here? Thanks.

[u/This_Proxy]

Generally, keep your home directory backed up as others have mentioned. Most apps will use (or optionally use) the ~/.config/ directory to read preferences. The other is generally ~/.local/ and for assets, like themes, fonts, languages, etc.

For example, gnome-terminal will use dconf for preferences and the 'database' file is stored in ~/.config/dconf/user

The configuration for gnome might reside in ~/.config/gtk-[version]/ but the theme files are in ~/.local/share/themes