Hello Michelle,
May I answer your last question first? Oh my goodness! Your 'Ohana experience may actually better than you could have ever imagined! According to the
online calendar, Wishes, the Magic Kingdom fireworks show, is scheduled for 10 p.m. that evening. Now remember, times are subject to change, but if this remains, you will have a wonderful view of it all! At 'Ohana, they dim the lights and pipe in the music so you won't miss a minute of the show. It's awesome.
After all the excitement surrounding dinner, I have three suggestions for getting back to your Resort. You could take the Monorail back to the Magic Kingdom and take a bus back to your Resort from there. Or you could take the bus to Downtown Disney from the Polynesian and then hop a second bus to get to your room. Or you simply can take a cab.
I hope you have a magical dinner. I think it's going to be a wonderful experience!