Re tents - flat rock Is the one nice spot to dump and sort your gear and chill after the walk up. Sticking a dome in the middle of it so you can be comfy is just fking inconsiderate to the majority of people camping below. And I would add is completely missing the point of the experience of bivvying in the pound
Re water - most of the time there is a flow of water to top up the tank and I'd suggest that most times of the year you'd be hard pressed to empty it - especially the time of year Ben appears to have been up there. Despite this I did say "careful use of water" and 2 weeks 7 people up there is not only "not careful" I doubt it would be much fun - for that sort of trip chilling around a fire at bottom camp is way more preferable.
Re water2 - cute thought experiment. But I have spent 6 - 8 weeks bivvying near top camp (not at it as funnily enough I never have and never will as there are many better places to stay) with minimum 2 of us but up to 6 at the worst time of year for water flow ( ie autumn) which also included the Easter weekend. This was also the time of the old galvo tank. Only right at the end did we get close to the bottom and not that it was foreseen that way but it turned out to be a great time to clear out kilos and I mean kilos of sediment, sludge, dead lizards and more dead lizards (that's not a joke). We were back there a month or two later once winter hit and it was full and clean again.
Re your fecal obsession - moonarie is big, people that climb there are few. All in all the fecal load will be at bottom camp as most people stay there so a bit of spreading it up the slope can't be bad. If anything bottom campers should be encouraged to squeeze in that morning post coffee shit until they are at least a bit up the track. Sure you need to be sensible but all in all i'd kind of be happy if shit got to be a problem up there.
Re gear - he asked whether there was anything gear specific. There is nothing. I concede the two sets of wires might be handy but ain't necessary with overlap on cam sizes. RPs or equivalent small wire are essential if you have an aversion to dying on a lot of the face routes over grade 20 - you can get away without a lot of the time but not when you need it. I would be a cripple or dead without RPs on the Great Wall. Finally I've climbed a high percentage of the main routes up there and I have never ever ever taken more gear than what I recommended up a route.
My advice was based in the premise that if you are a two set of cam person you are a two set of cam person and therefore shouldn't be asking or offering advice.