We stayed here in December and yes, it is feasible to walk to both Seaworld and Aquatica. I would even go as far as saying that for Seaworld, walking is the quickest way. For Aquatica, we took the I-Ride Trolley there as we had passes anyway and walked back.
As far as Quick Queue is concerned, we had to get a confirmation number from the Expedia desk, which is at the far end of the lobby and then used this number in the self-service ticket machines at Seaworld.
Corinna