You can select your BA seat when you check in online, 24 hrs before the flight. With their 767 you never know - you may end up on one of older long haul configs with older style J seats (those with fan partitions). Happened to me in September on LHR-ARN, we were pleasantly surprised though the IFE was not working
I'm not too fussed - it is an hour flight.
Looking at the lounges - it looks like Amsterdam doesn't have showers - which is a pain. I note T5 at LHR has an arrival lounge, however it is only for longhaul travellers - I'm wondering whether they will consider me longhaul coming via AMS from HKG