Welcome aboard, Juliane! Isn't it exciting to begin planning your very first cruise with Captain Mickey and his crew? No matter which ship you choose, you're in for all sorts of magic and surprises when you set sail with Disney Cruise Line.
You mentioned a sailing from Miami in late October. That is the Disney Magic, and no it is not scheduled to include Key West as a port of call on it's cruises around that time. However, if you're flexible with dates and really want to include Key West, the Disney Wonder will be making a port stop in Key West on all three of it's seven-night Bahamian itineraries in November of 2015. These cruises set sail from the home port of Galveston, Texas, and also include port stops in Nassau and Castaway Cay.
My family has sailed with Disney from Galveston twice and found it to be a great home port and easy to sail from, so that is always an option, Juliane! But, believe me when I say that the magic of sailing with Disney isn't necessarily in which ports you visit, but in the experiences you'll enjoy onboard. Castaway Cay is also a fabulous beach and of all the ports Disney visits, it is certainly my family's favorite, so I know you'll enjoy every minute there, whether you also visit Key West or not.
No new sailings will be added to the 2015 schedule, but there will be additional 2016 summer and fall sailings being released soon! Perhaps one of those will include Key West as well!
Have fun planning, Juliane!