1) The difference between Composite 8.0A and 8.0C is the 8.0C is newer and will have additional composites that are not in 8.0A

2) Have a look at the *OE Ord Head w Cust, Terms composite table from 8.0C, I believe it has all the information you need.

3) You will need to define a Calculated Columns using the information from the table. Adagio tracks Invoice Total, CN Total and DN Total. Use GridView to show them all and then determine what your formula needs to be.