Whoo Hoo! Great choice! It'll be really nice to be at a monorail resort
I'll refer you again to tikiman's website for lots of info about the Poly
http://www.tikiman2001.homestead.com/index.html
I'm sure lots of people can help you with requests. We stayed in Fiji, on the third floor, looking over the marina. We could look directly across into Ohana's. It was a very short walk to the main building and monorail. I liked the room location a lot, the only thing was if anyone wants to sleep during the day - the marina can be a little noisy. Your kids are old enough they probably won't be napping in the afternoon though.
Of course first you'll have to decide on what kind of room you're going to book (as far as garden or lagoon view etc), then think about what you want to request.
If you plan on doing any sit down dining, call for priority seating times as soon as possible.
Are you going to split your stay with a Universal hotel? We have done that.
Yep, you're going to have to call Disney to book that code. You can't do it on Disney.com. Here's a #: 1-800-421-3732, just tell them you want a room only reservation with that code. It will have to be available - they only release so many rooms at that price. I haven't used
Dreams Unlimited but have heard good things - if you want to let them handle it.
Good luck and have a great, MAGICAL time!