- PhysicalInventoryCount is the BO for InventoryCount. I see it has WriteAccess. But, you will not be able to develop a "Create" webservice for it. So, you need to have your customBO with the same structure you want in PhysicalnventoryBO's instance and develop a webservice on your CustomBO.
- Take the data from Incoming calls and create instance of PhysicalInventoryCount in your custom BO's actions. Your Custom BO doesn't need to store anything here.
- I don't see a way to implement InventoryAdjustment.