yeah, the name has to be a minimum of 4 characters long. 16 Mac and the first name will not be available, here the game is lying to you because the name will never ever be used.
Regarding point 3, it seems you ran into the door bug or else I don't know what you are referring to. There are a lot of levels in the tutorial and you learn really nice abilities. Please give the windows version a try. It has less bugs, don't know why.
I really don't want to get a bad rating due to this stupid bug.
I don't know why your pause button did not work, it should.