This is a great question! You need to determine how many days you need to do the things you want in each of the parks. You want to enjoy them NOT race through to say you did them. Take the time to take in EVERYTHING in each of the parks, each of the rides, EVERYTHING. As they say “take time to stop and smell the roses”.
This question is first answered by how many days in your vacation. Then what you want to do and see. You can spend a whole day in the park or a partial day in the park (dinner and fireworks only-maybe sneak in a ride or 2 then again you could go in first thing in the morning going on your favorite rides then leaving before the crowds get there). You may start in one park the “hop” over to another for a special dinner or show. You have so many choices!!
As an FYI once you get past 5 days of parks, the price per day goes up a small amount (example a 5 day ticket is $58/day where as a 10 day ticket is $40/day). Also, to add hopper option is flat $69, you can add this onto your ticket once you are there or in advance.
Hint: Magic Kingdom has the most attractions, so probably need extra time here.