In addition to your concerns, I was worried about just being on a plane for that long a time without going stir-crazy but it worked out pretty well. This was mostly thanks to suggestions and recommendations from FT.

Have ambien, lots of water and comfy clothes for the flight. I also had the noise cancelling headphones and my own sleep mask to use. I took the ambien at the end of the meal service (early morning hours HK time) and slept for 4-5 hours, took a walk to stretch a little (first time on the 747, I wanted to check out the downstairs and was glad I was upstairs ). I napped on and off for the next couple of hours and saw bits of all the movies they were showing (didn't need to use my own DVD, they had enough of a variety for me). When they served the second meal I freshened up and by the time the plane got in was ready to go. After a quick shower at the hotel, I met up with everyone for dinner around 9 and lasted till 1 am.

For the rest of the weekend, I was fine (this was my biggest time change). Though I do have to say that I slept VERY well on the return flight so it was starting to catch up to me at that point.

Have a great trip.