The big thing in planting corn is being able to detect skips...when a seed is supposed to be dropped yet not. This is usually due to the vacuum pulling a seed against the seed plate not being correct. So I really need to be able to measure population based on seed drop from the seed sensor, display it on my Android UI and also throw up a flag on the UI when a skip is detected also.
Pulse counter connected to PIC for serial communication looks the way forward. Have one pulse counter and PIC for each row. Just need to test a pulse counter that works with the seed drop pulse. I have used this for example CD4520BEE4 it counts in the background and outputs the count to four pins on the PIC. The count is simply read by sampling the port. They are cascade able so can be connected to give 8, 12, 16 ... bit counts. The PIC will read the port and send to the UI, which you have already sorted out.

I presume that as there is a PIC on each row it could also be used to control the motor.