I also have about four photo resistors
About? Does that mean somewhere between 3.7 and 4.3? 
various digital pins with a pull down resistor.
What size resistors?
Should be very simple circuits right?
Yes.
I want to make sure that my wiring isn't stressing out, or pulling/pushing too much voltage that would fry my Arduino
Voltage wouldn't be the problem. Current might be, but the switches and photo resistors should not draw near as much current as the ethernet shield.