My #1 tip for a faster Vendor Invoice entry is to use standard purchases codes and to add this code in table 38:
Vendor Invoice No. - OnValidate() UpdateInwardHeader; //>>New code StdVendPurchCode.SETRANGE("Vendor No.", "Buy-from Vendor No."); IF NOT StdVendPurchCode.ISEMPTY THEN StdVendPurchCode.InsertPurchLines(Rec); //<
If you also put Due Date on the General Tab life get's more easy.
Its a pity that you cant move fields between tabs as user config/personalization. We still have to modify objects to accomplish that.