GNOME has an entire extension ecosystem. Look up “gnome extension manager” on flathub.
Yes, Linux can be more problematic on some laptops. Especially ones with realtek wifi/Bluetooth or Nvidia/Intel hybrid graphics.
Yes, try EndeavorOS.
Linux gives you the full power to delete whatever, whenever. You can delete anything and everything you want without needing any workarounds.
No. Linux by default gives you root access. It’s a thing you just get. In fact you need it to update most* distros. You don’t need to “root” Linux. Root privileges are a given on most distros.
Install the other DE’s package from your distro’s repos, logout and the login interface should have an option to change your DE, the next time you login.
It’s… Complicated. TL;DR Wayland is the more modern display server that most distros and desktops are in the process of moving to. I’d suggest using it over X11, wherever possible. As for docker, that doesn’t really matter for desktop use.