Thanks for asking. I was kicking around the idea of upgrading my girls' 2-day hoppers to APs and it would be nice to be able to use gift cards. Glad to see it's doable and when to try the lines!
No problem doing this at the ticket booths and no limit on the number of gift cards you can use. (We've used quite a few for one transaction and had no issues at all.) Lines at night are usually fairly short. Be prepared, though -- if you get a new CM, the transaction might take a bit longer than usual.