How to plan your fastpasses when park hopping? This is a great question.
Some people want to hit two parks in one day. This can be great fun (yes some people even try for all for 4 parks, but that is another story).
Plan on park 1 to be there for opening and hit your must do rides. Then you would go to park 2 where you would have chosen your 3 fastpasses for. REMEMBER once you use your 3 fastpasses you can pick a new one.
Another way to do two parks is use your 3 fastpasses for park 1 then go to park 2 pick your 4th fastpass, use, then your next fastpass.
I prefer option number 1. You should do what is best for your travel group. Enjoy!!