You still need to make an ADR for Hoop Dee Doo, and pick which tier of seating you want. Without the DP you'll also pay for your reservation at time of booking.
When you make your Fantasmic Dining package you need to tell them it's for that package and then they will tell you what times are available for meals. They tend to be afternoon (2-4pm) times though, so be aware it won't be normal dinner time. Then you arrive at the F!DP entrance (by Tower of Terror) about 45 min before the start of the show.