Oh, where to start. . . I love talking about Disney World!!!!!
It is totally appropriate to bring a 10 month old in my opinion. We brought our 5 week old this spring. Most of the rides in Magic Kingdom are baby friendly. I was able to wear Aiden on everything he rode. We nursed on a lot of the rides, too. You will be able to find baby friendly rides in all of the parks. Disney doesn't have any weight requirements. One ride I found had an age requirement which was the Indy Cars at Magic Kingdom. The kids have to be at least a year old. They have height requirements for the faster rides, you have to click on the individual attractions on their site to get that info. Here are a few links for you:
http://disneyworld.disney.go.com/wdw/parks/parkListing?id=MKAttractionListingPage
there is a list of little kid rides on that page and links to all of the individual ride pages
http://disneyworld.disney.go.com/wdw/parks/attractionDetail?id=SpaceMountainAttractionPage
http://disneyworld.disney.go.com/wdw/parks/attractionDetail?id=BigThunderMountainRailroadAttractionPage
http://disneyworld.disney.go.com/wdw/parks/attractionDetail?id=SplashMountainAttractionPage
these are links to the Mountains that show the height requirements
Another really helpful site is www.allearsnet.com
As for carriers, I am a heavy packer! In April (a bit cooler than when you are going but still 91 everyday) I brought my Jullian didy, freehand mei tai, hotslings pouch, and solarveil mei tai (thanks again JoLynda). I would totally take a solarveil or solarweave if you can get your hands on one. I think the solarweave would be more comfy for all day since the fabric is so much softer. I ended up wearing the didy once and getting really over heated. We were only doing FCC, so we had too many layers, it may work with a rucksack. The mei tai's were very comfortable to wear for long periods. I used the pouch for quick trips because I am not very comfortable with the weight on one shoulder for long walks.
You are going to have so much fun!!!!
HTH, let me know if you have any more questions!
Stacy :)
Mom to Garrett-2.23.01- and Chase-9.30.03- and Aiden-3.15.06