Just to know if I understood right, using all 4 motors would require more current over using 2 motors. Could the load/weight increase require more power on 2 motors over 4 motors?
Using 2 motors will use less current. However if the buggy is too heavy you might need 4 motors to move it. Since there does not seem to be any speed requirement if you run the buggy on a flat smooth surface you may well get away with 2 motors, try it and see. You could put 4 AA batteries in the buggy and put weights onto to it see what is practical.
If the motors cannot freewheel, and you want to use only two, then you will need to attach a couple of wheels without motors.
Regarding the LDR; The iodine clock reaction turns the mixture from clear liquid to blueish black mixture. It pretty dark, Think the LDR could pick up the change?
Yes.
Bahrain used to export sand until they started to run short.
Tiny is;and really. I don't know what they were thinking.
Yes, it seems the world is running out of sand. That is why your neighbours in the UEA are such big importers. In the Philippines several islands have disappeared completely because of 'sand pirates' stealing the stuff.