ONLY DATA MIGRATION responsibility :
i will provide best solution data migration with diffrent phases and with creating mapping sheet. i'll share the mapping sheet with migration plan creating re-concilation script and helth check for testing with loading data. i'll provide the complete SSIS packages , re-concilation script , post run scipt , helth check script for future pupose. client can do the migration with runing ssis pachage then run the helthcheck.
i will start working on three phase in first phase i'll delivered 20% of data , 2nd phase 70% of data and then final phase full migration. after each phase client can check the data through there front end software.