You should make your request when you make your reservation, if you are not ready at that time, then call back as soon as you know what you want. This way the request can be noted on your reservation.
Calypso is the closest building to the main building with the foodcourt etc, and it is a great location. I've stayed in the Jazz building as well and the walk from there is not bad at all.
Ask for one of the Calypso buildings, it can't hurt to ask, even if you get a location in one of the Jazz building you will be fine.
My suggestion would be to request a location facing away from the pool. It can get rather noisy with the music and games and the movies at night.