sub contracting process between company codes

Dear All

I want to map the following scenario.

We have 3 company codes under one client.

1.Company code A has one plant say plant ' A '

2.Company code B has one plant say plant ' B '

3.Company code C has two plants say plant 'C' and 'D'

4.we have already implemented SAP in Company A (plant A) and Company B(plant B) ,Now we are going to implement for Company C (plant C and plant D)also.

5. Right now, both the companies A (plant A)and B(plant B) are giving the job work to the Company C (plant C and D ).The Raw materials which are required for Job work are provided by Company A (plant A)and B(plant B).

6. Currently we are considering company C (plant C and D )as a vendor,Company A (plant A)and Company B (plant B) following pure MM Subcontracting process.. {creating PO, Subcontract Challan and MIGO}.

7. Company C (plant C and D ) is doing ONLY job work for Company A (plant A) and Company B (plant B ) only ,not for others.

How to map this process in SAP,what will be the PP process in Company C (plant C and D) ,

A).Which Strategy to be used ?

B).whether costing is required or not ?

C) As we discussed above Raw materials are provided by companies A (plant A)and B(plant B) to plant C , 50% job work is done in

plant C ,then those materials are sent to plant D to perform remaining 50% of work ,how to map this cross plant manufacturing process.

Here I am requesting you, please give me your valuable inputs...waiting for your valuable replies.

Thanks & Regards

prasad.p