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.