I'll caveat what I'm about to say - I'm not an expert on KEHS uniform. I took our son to be kitted out for CHB so I'm fairly clued up about that one, but I stayed well out of the way when it was our daughter's turn.
That said; as far as I know the skirt/trousers are supposed to be the official ones with the little white rose, I don't know if they rigorously insist on that (I think it was mentioned at the parents induction meeting) - and it's invisible anyway when they roll their skirts up (yes, even KEHS girls roll their skirts
Mountains of sports gear seems to be common to all, and especially girls schools. By the time you’ve got the leotard for dance, the skort/ Astroturf trainers/shin pads/polo shirt for hockey, the shorts/top/non-marking trainers for PE, the tracksuit, the swimming costume…it makes you wonder whether there’ll ever be time for “real” lessons. Now that I've got two at secondary and have a slightly more jaundiced view of how much of it actually gets used, I recommend finding a PE teacher at the induction meeting (in fact I'm pretty sure head of Y7 is PE - can't remember her name I'm afraid) and trying to get a sensible answer about whether you can get away with not having all of it, or at least not all at the start. If you don't get anywhere with her it might also be worth talking to Early Years to find out their perspective - they sometimes have better information than parents about what's actually necessary (certainly for CHB, don't know about KEHS). Daughter is not doing hockey AT ALL in Y8, so really I don't feel I'm getting my money's worth out of that bit of the kit – and it certainly won't fit her by Y9
And definitely turn up for the second hand uniform sales, some very posh ladies indeed were rummaging through the sweaters at the one I saw.
Trips etc: there is a residential early in Y7, about 3 days or so, which costs somewhere in double figures if I remember correctly, and a few trips during the year. Most are local and cost very little, although there was one to the Space Centre in Leicester that was well into double figures. Towards the end of Y8 there's another residential, four days and a couple of hundred pounds I think, but not everyone is going on that.
I haven't seen any mention yet of things like skiing trips which tend to be the really major ones, possibly daughter doesn’t fancy skiing. There are some expensive possibilities further up the school but I haven't had to worry about them yet, and if your daughter gets into the symphony orchestra/senior choir there's an annual residential for that plus tours. I imagine there are also the usual sports tours for those on school teams, but that aspect will never trouble us. There’s a trips/holidays page on the extra-curricular section of the web site that outlines the opportunities/threats.
“Other people”: The personalities are much as you'd get anywhere: the "Winterbourne" set (hang around the equivalent of the bike shed to flirt with KES boys), sports obsessives, nerds, musicians, arty people, stereotypical rebels, etc., etc. As is the way with teenage girls our daughter blows hot and cold about various individuals at different times, but she seems to like most of her year most of the time and appreciates them for their own strengths and weaknesses (which is an attitude the school seems to set out to develop). There is quite a mix in economic terms, from the multiple-pony-owners to people who are clearly finding it a struggle to get by, although obviously the comfortably off are in the majority. I find myself a little overwhelmed occasionally when collecting daughter from places with marble floors etc but she (and friends) seem indifferent to it all.
Homework: I find this hard to judge, our daughter is ultra-efficient about getting it done and will do it during break or lunchtime if there isn’t a club/activity she’s interested in, so we don’t see quite as much of it as we’d like from a nosey, interfering parent point of view. As far as I can tell, she gets about the same as our son got at the same stage (supposedly about an hour a day, give or take), but the difference in their approaches to it makes comparisons difficult.