Hi Mary,
I was able to tour
Disney's Art of Animation Resort recently, which is I believe the resort that you are speaking about. It is an amazing resort. The themes are so bright and incredible!
You will be able to refill your refillable drink mugs at the Landscape of Flavors, which is located in Animation Hall, the main building for Disney's Art of Animation Resort. Although this is not right next to the Little Mermaid rooms, I was impressed by how easy it was to walk around the resort.
As you mentioned, since you are visiting Walt Disney World the week before Easter, the resort will be crowded. There may be times of day that you find the buses and Landscape of Flavors to be crowded. My suggestion is to use each at slightly "off" times. By eating a meal a little earlier or later than others typically do - say dinner at 4:30 p.m. - you can avoid a lot of the crowds. If you wait a little while after fireworks before going to the bus, you will find the buses less crowded than trying to leave immediately after the fireworks.
I asked a cast member at Disney's Art of Animation Resort, and she felt that the bus stop at Disney's Art of Animation Resort will definitely be closer for you than walking to Disney's Pop Century Resort.
As to the air conditioning in your room, each room is individually controlled by the guests staying there, so you can make it as warm or cool as you like!
I hope that this information helps to answer your questions, Mary. Please do not hesitate to ask if you have any further questions!