No. FiveM is developed exclusively for the PC version of GTA V. There are no plans to support consoles.
There are no plans to support the FiveM client on Linux. While some components may work, full functionality is not guaranteed. The FiveM server (FXServer) is available on Linux.
That depends on how you installed it in the first place.
%localappdata%
:
WinKey+R
on your keyboard%localappdata%/FiveM
in the dialog that opensMore about installing FiveM here.
Nope! As mentioned on fivem.net, FiveM does not interact with the Rockstar Online Services other than to validate your game copy the first time you launch it. This validation emulates the game's interaction, and can not be detected by Rockstar. It also doesn't modify your game files at all, even when downloading server assets, so you don't have to do anything to move between FiveM or GTA:O.
It's never fun to run into problems. Read the client issues manual for help.