RE: Restrict User from Posting Transfer Order
Try restricting access to these Codeunit.
Codeunit 5704 TransferOrder-Post Shipment
Codeunit 5705 TransferOrder-Post Receipt
Codeunit 5706 TransferOrder-Post (Yes/No)
Codeunit 5707 TransferOrder-Post + Print
Codeunit 5856 TransferOrder-Post Transfer