Check compatibility for all your programs before you move. Most Linux programs work on Windows but not vice versa. If you’re not in a rush, try switching to programs that have a Linux equivalent before you move so that you’ll have less of a culture shock. If you need any killer apps that don’t have a Linux equivalent you’re going to have to make your peace with that ahead of time, otherwise you’re just going to end up switching back.

KDE is a good choice, and Kubuntu should serve you fine; if you end up going with Kubuntu, I would recommend sticking with it for at least half a year or so before considering switching to something else, as that will give you time to really understand what you like and don’t like about how Kubuntu and KDE work.

Generally, when you use apt you’re installing from your distro maintainer’s software repository (aka Linux Mint), who will have personally vetted and compiled the software available. This is usually the best and most seamless option as it will continually update itself along with the rest of your system, but the software version from the repo may lag behind compared to the latest releases directly from Google. If you grab it manually from Google, it will be the latest version available, but it will be your responsibility to keep it updated.

ADB and Fastboot still work on Linux, e.g.: https://itsfoss.com/install-adb-fastboot-linux/