Lithium Battery Pack Discharger
Your circuit looks good. But you did not show how you are going to drive your MOSFETs which is the important part.
For this I have many thoughts that will not fit in this answer. I will recommend two for you: 


use LTC6804 chip from linear technology
or use Solid State Relay (SSR) instead of MOSFET


LTC6804 is an integrated solution that will allow you to measure each individual cell with balancing. SSR is a simpler solution with an isolated driving signal  which will greatly reduce your design complexity but will not help directly in voltage measurement.
Beware of how you will sense voltage using Arduino. I am worried you might wire a short circuit!