If you choose to use a TA, I would pick a TA who specializes in WDW travel.
There are many,
Dreams Unlimited, Ears to You, Mouse Fan, Instant Impressions, to name a few.
Is your cruise leaving from Miami as well as returning there?
I often book a multi city fare because I fly into Ft. Lauderdale first to visit family, and rent a car to drive up to WDW. Then I fly home from Orlando.
If you book the air yourself, the airline sites have a Multi-City option.
I prefer booking air myself, regardless of if I use a TA to book WDW. I like to watch the fares so I can get seat sales. Kayak.com is a good site.
If you book with a WDW specialized TA, they can book flights if you wish. They will also know when WDW is coming out with discounts, and will automatically apply it to your res. If booking yourself, you'll have to do the watching.
Good luck with whatever you decide.