We did EMH last september at MGM and it was EMPTY!!! The parks were all generally pretty empty during our trip but MGM was literally EMPTY...I have a pic to prove it (if I can find it, I'll post). We weren't able to get on RNR because they were doing "maintenance" or something but we rode Star Tours twice, did the Muppet 3D show and something else that I can't remember before the park actually opened. It was fun.
I think the easiest way to get to MK is by bus...I don't know if you can go directly there from MGM but we took our bus back to POR and then switched over to the MK bus (the POR bus happened to be pulling up as we were walking to the stop so we just hopped on!)
GOOD LUCK AND HAVE FUN!