how to wire together multiple photoresistors to make one big sensor?
I would take the following approach:


Measure the resistance of one device with laser absent and laser present. You will have two readings.
Mathematically model the circuit with all photo-resistors lit and then with two dark.
See if you think you can create a potential divider that will allow you to reliably detect the difference in voltage between those two states.


Post your readings and calculations in your question if you get stuck.

You will improve the rejection of ambient light if you add filters to the sensors. The filters should pass the laser wavelength - typically red - 
and block others.