Basildon

Can anyone please advise me on the 747 fuel system when the HS tanks are used. These I believe hold 10,000 kgs of fuel which is to me a large weight to be present at the rear of the aircraft so I ask the following. Is there high weight cargo placed forward of the C of G to allow for this, if so what happens wen the fuel is used as the aircraft would become nose heavy. As the aircraft also stores fuel a bit rear of the C of G in the wings how does this affect balance. I am really interested in the above and also how the aircraft is balanced for take-off with the correct setting of the HS trim as this appears quite critical. I have read about the MAC and understand it a bit but not fully. For an empty aircraft ZFW, where is the C of G and centre of lift. I thank anyone who can enlighten me on this subject as it truly baffles me.