AHHHHH! Dont switch!!
I have worked with AAA in the past and it is impossible to get in touch with your agent in a timely manner to make any changes. If you are booking well in advance, the AAA offers seem like a good deal, but Disney almost always comes out with e special promo a few months in advance of your arrival and switching to their promo through AAA is not easy. I called my AAA
travel agent the day the promo came out and she was out for the day. Disney would not even talk to me because I was not booked through them. I waited until the next day, called AAA again and the agent was at lunch, then in a meeting. It was day 3 I finally got through and my resort was already booked for the promo. I had to change resorts to get a deal. Awful feeling and experience.
I would never book through AAA again (at least for Disney). But to your question, yes, you can make several payments on your booking. Final payment is due 45 days in advance.