For random orders by a customer, you may use the Event-Based Entity Generator block coupled with a Random Event Generator(Random Number -> Gateway). You can use a combination of flushable Queue-Server with a Single server to do the order to shipment conversion.
For determining the number of orders placed, enable the Number of entities departed(#d) in the block parameters for the initial entity generator block. Same goes for the Shipments server block.
In both of these blocks, It can be enabled by double clicking the block, going to statistics tab and selecting the appropriate checkbox.
