Congratulation on new toy.
I still use old IE under mac but every time get that security warnings makes me to think twice to do something serious on it and as you said, Microsoft site refers you to use Safari.
If by screen size occupancy, you mean the size of window in mac, you can adjust that as you need by holding the mouse bottom (Don't ask me which bottom
) when pointing ONLY to the right lower corner of window and dragging to the size you like, unlike windows that let you use any border for this function (And people think mac is smarter).
Welcome to the New platform syndrome. Patience is strongly advised and helpful for next few weeks