"I understand they are high maintenance, but how high?"
I'm used to dogs, so not as high as that, lol...they like to be with you, they'll follow you about and investigate everything you're doing and you'll never sit down alone again.
As already mentioned they chat a lot, but that works out fine if you're the sort of person who talks to themselves anyway
I'm forever wandering round my house going, what was I looking for? Now a cat answers. They'll also swear at you if you do things like go out, but you just accept that they're going to do that for a bit when you come back.
"Do they get along with your average moggy or are they on a different planet?"
Mine gets along fine with my moggy, it took a while, but it wasn't as dramatic as other people introducing two moggies have had, she spent about 6 weeks going, nope, I'm not being near that thing...then a couple of months going well I suppose I can put up with it if it leaves me alone and within a year they were pretty friendly, they sleep together if they're on the same nap schedule, occasionally play together and the moggy brings back mice for the Siamese (she doesn't go out much , because...weather) but the moggy is not allowed to sit with me, I belong to the Siamese, lol .
"Do they tolerate children?"
Mines much better with children than my moggy, she's not hugely keen on toddlers because they're rough and leak water (wet is bad) but she just sits where they can't reach her and happily spends time with older children, she actively likes being picked up and carried round so that's quite compatible with children and has very rarely bitten or scratched anyone other than when playing.
She's actually very sociable with visitors and really quite laidback about things like getting vet treatment or giving pills, so not high maintenance in a temperamental way at all, just... needy, lol.