I have not found it to be any noisier at the back of the cabin in a 747, except maybe at takeoff. Now if it was an MD80 then things are very different! But you can always take some ear plugs with you just in case.
This can be an issue just after meal services. But generally not too bad at rows 70 and 71. You will get a reasonably constant stream of passing traffic, but that is par for the course almost anywhere in the economy cabin of a long-haul flight.
This is minimal under smooth conditions, and some find it helps with sleeping. But you will feel turbulence a little more than someone sitting over the wings. But if you think of the aircraft's centre of gravity as being the pivot point for the "wagging" (i.e. close to the centre of the wings), then those sitting in row 1 are going to be feeling the same (but opposite direction) wagging, and we know that lots of people like to be sitting up near row 1!
Yes, this can be a concern. However, you will be spending something like 20 hours sitting on the plane and maybe 15-20 mins queuing for immigration. Which is most significant? And note that most people who get off the aircraft first and through immigration quickly end up standing waiting at the baggage carousel for their bags anyway.
I would certainly consider those seats if travelling with 2 kids. The alternative is a block of 4 seats in the middle. But most kids like to have a window seat so the middle block is not going to be overly kid friendly.
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