Hitler was a superintelligent little man with a twisted mind, very dangerous. The term Führer is not something he made up, however, but he chose cleverly.
I don't know.
Roy also seems to have to do with fire, but "king" is the only translation from a language I can get to. But many story characters (anime/game stuff) that do something with fire are called Roy for some reason.
Like the guy from Fire Emblem.
And I used to know more of them but I seem to have forgotten about them.
By the way, "roi" is French for king, too, so it's also from modern languages. XD
And personally I think "Roy" has a much nicer ring to it than "King" especially since "King" is Führer Bradley's first name. And they pronounce "Roy" so nicely in the series.
And dudes, don't go and inflate the guy's ego. I have a Roy figurine that has a nice view of what I'm reading right now. X_x;
I bet the Ed figurine is laughing his ass off, however.