If you decide to stay in WT+, then 12A/B or 12J/K is your best bet. Yes, they have bassinets, but you get good leg room. As there's only two of you in those seats, you won't have to "climb" over each other to get to the toilet (or rear galley for a top-up of wine...)

There's one meal service. To be honest, I'm not 100% sure whether it's dinner or breakfast as I haven't operated this route yet, but I'd hazard a guess at dinner.

There are various reasons as to why the 777 is used on this route. Some are facts, some are more towards the rumour side of factual. BA wanted to use the 777 to be different (I guess for the discerning traveller). The other aircraft we operate at LGW aren't really suitable for such a long flight (IMO). I don't want to imagine such a flight on a 737 (PFO is more than long enough...).

The night time slots were the only ones available, although I personally think that as and when a day time slot becomes available, this will be utilised. There are talks about new long haul destinations coming to LGW soon, so the aircraft can be utilised on these routes when not doing the SSH route.

I'll try to get hold of a friend of mine who's operated this route a few times, and I'll let you know asap. Hope this helps.