Hi Rajat,
Regarding your first scenario:
We also have a small manufacturing unit, were we do manufacturing of PCB's. This is basically assembly work, were in we Orded Raw materials i..e components required for PCB's as per project requirement and do assembly in house and sell them to client as a finished unit i.e. Finished PCB's. There is Fix BOM for these PCB's.
-I hope if you assign the BOM with header material(Final product -PCB)as (-1) qty this will serve the purpose.I assume that the line items are all of procurement type(F) and after MRP run(MD51) it will generate Preq for line items. No requirements will be generated for header material as it is attached with (-1)qty and this can be GR against reservation.You will need to explore little beat on this.
As you are not using PP module , for sub assembly performing you will need to book labour charges that can be done on internal activity.
Regarding Third scenario:
Our requirement is Order Raw material against project/order, have FG stock against project/SD order and delver this FG unit to client against which billing has to be done. Cost booking will be done against project in case its project requirement and against SD Order if its only supply order and not for project.
-Here you can linked(input) WBS while creating sales order.Project based delivery can be done and billing can be done via Sales order.
Regards
Nilesh