There are several constraints on which schools to apply to and how many to do so:
1. If this were the only school you were admitted to, would you want to attend the program? If yes, then the school makes the list.
2. How much time will you have to complete the secondary applications? Going through secondary applications can be a grueling process. You need to start now if you have not done so. A few schools make their secondaries openly available - make sure you start of them now. When does school start and what kind of classes will you be taking? Will you have time to complete the secondaries while fulfilling your other obligations.
I would apply to as many schools which fulfill constraint #1 for which you can finish the secondaries in a reasonable time. Otherwise, you are just wasting your money.