Try Magic Eraser Sponges, available at most stores that sell cleaning supplies. They really ARE magic for things like this very often! Worth the effort.
Probably not, plus it will get worse over time.
I've an old George Foreman with similar marking.
Neither oxygen nor chlorine bleach works - plus it smells.
The only thing that very slightly works is a good hard scrub with something quite aggressive, oven cleaner or barman's friend etc, which will eventually take all the paint off.
You'll just have to live ...
Yes it is safe, all microwaves work on the same principle, and use the same range of radio frequencies to heat food. All microwaves used to be flatbeds, most commercial microwaves are still flatbeds, so you have nothing to worry about.