One global location is sufficient for the three organizations.

Three lines were set up on a sourcing rule and the sourcing rule was assigned to a single Assignment Set.

A sourcing rule is set up for a supplier but no ASL. When an item is entered on a requisition for this supplier, the supplier information would not be defaulted.

The price for item A is set in ITA at P1 and in GER at P2. When you raise an internal requisition for item A in destination org ITA and source org GER, the defaulted price is P2.

ITA has a sourcing rule to source a part from GER. You also assign a bill of distribution to ITA to source the same part from the manufacturing plant NYC. The default source would be GER.