Welcome to planDisney, Susan! You sound just like me: I am always trying to get the most out of my time at Walt Disney World Resort. One Theme Park per day just doesn't do it for me, and I always find myself at two or three before the day is over!
Susan, I don't see any issues with your plans as you have them now. If you want to start the day at
Disney's Hollywood Studios, hop over to
EPCOT on the
Disney Skyliner or
Friendship Boats, and then come back for an evening viewing of
Fantasmic!, that's totally fine. Your
Fantasmic! Dining Package does not require you to stay at Disney's Hollywood Studios all day. If you have a Park Hopper ticket, you're free to go wherever you want when Park Hopping starts at 2 p.m.
Your Fantasmic! Dining Package entitlement will have specific instructions about when to return to the amphitheater to make sure you're admitted for the show. Currently, the seating area for guests with dining packages opens 90 minutes before the show and you are requested to be there at least 25 minutes before showtime. This is subject to change, so be sure to double-check when you're having your meal so you can arrive at the appropriate time.
Have a magical day, Susan!
Jessica