Unless I'm missing something, I'd say make the atmega do all the work. It can read the shunt and battery pack (and half pack?) voltages directly on the analog pins. external circuitry is still a couple resistors and some zeners.
EV definitely merits some personal attention.
It will take a little more care in resistor selection though, you want to wind up with a voltage divider that peaks at close to 5 volts at the atmega for the battery pack monitors and the motor shunt (maybe just trim pots). Might be nice if it has an onboard charger to monitor the 120 input also, and vss of course.
analog connections so far:
1 battery discharge shunt
1 battery pack
1 onboard charger input shunt
1 *battery half pack (to detect gross battery problems)
1 *aux battery
digital connections:
1 vss
3 buttons
8 LCD
And, well, I think that takes up all the available pins except one analog and serial rx/tx
