Hi Ajit,
I would question the need for two company codes in your scenario. in normal business your company code 7000 will be set up in the system as a production plant instead of a company code. you may want to talk with FICO consultants and avoid having a separate company code created for 7000.
As for your questions, what process you need to take depends on the business requirements as it comes to FG consumption process, how they want to post cost and revenues, how they want to handle credit, pricing, delivery, et al, there is no way that you can get an exact answer here since this is really a design question that is dependent on the client business.