Do we have to do any coding?

What effort is required to integrate this Audit Trail in our application? Do we have to do any coding? For e.g.. Say how audit trail will be updated when a new invoice is created / modified/ deleted? Do we have to call some procedures of audit trail from our program and pass values as parameters? If coding required, what would be the volume?

You have to do absolutely no coding. Every ABC or Legacy operation will be automatically recorded.