One_:
If that diagram is correct 2 pins will be used for the servos, which will mean I'll be able to use the rest of the unused pins for my sensors. Is this correct or am I missing something?
Looks okay so far. You mentioned a 3rd servo and you'll need an analog input for each of your Hall effect, piezo and light dependent resistor inputs. The answer to your original question now relies on the number of LEDs you want.
Geoff