Measure Quality not Quantity
I would stay away from measuring the minimum number of calls handled in a day as a metric. You may look at it from time to time as a way of identifying performance problems, but you must back this up by call listening and looking at other metrics as well.
It is important to really focus on Quality not Quantity.
The problem is if you are looking at number of calls then that is only one step away from looking at AHT. It can easily send out the wrong message.
It is better to do fewer quality contacts than lots of mediocre contacts.
You still need look at people who have training needs or who are avoiding taking calls, but you need to be very careful about performance goals based on volumes.