Delete ledger entries


I'm migrating a company from Dynamics NAv 2009R2 to NAV2015. I'have a specific request.

We don't want to delete all Item Ledger Entries (they will do inventory to have a clean stock). We don't want to recover the accounting entries made before 01/01/2017.  (We  keep only open entries)


Can I delete the Item Ledger Entries with a DELETEALL without problems? what are linked tables that I need to delete or update also ?

Same for accounting entries, which related records do I have to pay attention to? Is there an adjustment to be made via sheets?

Should I do this before or after migration to NAV 2015?


Thank you for your help.