Nah you can have x3 load per core without problem. The real problem is when you haven't got enough ram xD

If snap or flathub repos are in the store, any mainstream application be in. In the other side, if you don't know what are you doing and install random packages, the most probably is that you'll broke your system

The normal people doesn't install software external to the store or configure the system a lot, in IOS you can't do this things and everyone is fine. For share network in gnome you can do it with a button in the WiFi settings

In my firs time with linux I install ubuntu (maybe 12.04, I dont't remember, it was gnome 2) in the only PC in my parents home, I delete windows, and we was using it 2 years without knowing what is a terminal and everything went fine, the problems appeard when I was discover the terminal hahahaha

In my opinion the hardest thing in linux is leave to use propietary or exclusive software for windows, the first think you must do is leave to use propietary software in windows, and when you can live without windows exclusive programs, switch to linux. You can start for ubuntu or other linux friendly distribution, doesn't care, afther the migration you can try other for curiosity without risk