As a rule of thumb, with talented team consisting of 1 coder, 1 modeler and 1 skinner, you should count on 1 model completed per week on average...
The reason why so little mods get finalised is because people neglect to do some simple math and let their wild dreams get the upperhand....
As far as the workload distribution, my experience is that texturing is the most time consuming element, followed by modeling, rigging and coding.
To give you some perspective, having the unit's code done is about 15-20% of the work....