You don't mention exactly how much assistance you require. The Club World window seats require a fair bit of clambering over people on both aircraft. If this is an issue for you, I would choose the Upper Deck aisle seats on the A380, probably Row 51 or 52. Easy to get in and out of, and in a fairly low traffic area of the plane. Otherwise, any Upper Deck window seat in that forward cabin will be great. They're as silent as you'll ever get on an airliner. Other than recommending the UD on the 747, I don't fly that aircraft enough anymore to really remember.

Meals are served shortly after takeoff, and then again breakfast just before landing. There is a snack corner you can access in between but it tends to run out of choices on the very long hauls.

I am afraid I have only used assistance at LHR, which to be honest was awful. But that was for someone who couldn't walk unaided.