We took our son at 7 1/2 months for the first time, so here is my advice from personal experience:
-A front-facing carrier: I love my Ergo too, but I bought a front-facing carrier specifically for the Disney trip (I think I found it at Ross or on
Amazon for around $25). It was great for waiting in line, getting on and off rides (not having to hand off the baby), and it allowed the baby to sit comfortably on my lap and see everything on the ride, without worrying about squirming. Definitely didn't have as much support as the Ergo, but we only used it in lines/on rides.
-Stroller: Definitely take a stroller! And I agree about one that reclines/has a good shade cover. My son kept to his normal nap schedule and took two naps in the stroller (maybe try this at home before if he hasn't slept in it before). On this trip we just did a day at the MK and were there from 9 a.m. - 5 p.m.
-Backpack instead of a normal diaper bag: We bought a regular backpack to use for the trip, and it was so much easier than our regular bag. Wear it waiting in lines, and never any issues with taking it on rides/into shows.
-Mom/Dad rides: While the baby is napping, do some rides you and your husband want to do. For more popular rides with longer lines, like the mountains, make FP+s around the baby's nap time. Also take advantage of baby swap - otherwise you are sitting around waiting for the baby to wake up (b/c you can't take the stroller into any of the indoor shows).
-Memories: Get your baby his/her first pair of mouse ears at the Chapeau on Main Street with their name on it. We did this before his first meet with talking Mickey at Town Square.
-Best rides: At the MK, our son most enjoyed Dumbo, Small World, the parade and meeting the characters.