linkffn(Dodging Prison and Dodging Prison) has a fantastic AU wizarding culture. It uses canon knowledge everywhere, but the author expands on it significantly to make it more "believable".

F.e. there is something called the "polyjuice defense" in that fic:

"It's a legal defence. Because polyjuice isn't illegal and is readily accessible for the right price, it's impossible to convict someone of a crime with eye-witness testimony alone, unless you can catch the person red handed and then hold them under surveillance for an hour to make sure they're not under polyjuice."

Or how the wizarding children spend their holidays:

Close to three dozen wizards and witches zipped about above them on broomsticks — some of them looked younger than they were. On the field in front of them, several groups of children and teenagers, and even adults, were engaged in all manner of magical activity. The wizard from the shop hadn't been joking — quodpot and snap, yes, but also wizard chess, bowls, and even what looked like competitive transfiguration. A pair of abraxan horses were tied up off to the side, grazing on the lush grass, and resting under a tree.

Appleby-in-Westmoreland had thirty-five magical children of Hogwarts age. Of those thirty-five, only six actually went to Hogwarts — the others went to one of the other three schools down south.

The only problem that most MC's in this stories are Mary Sues, which some people don't like. Combine it with an implied harem and it becomes even worse. If you can look past that, you'll definitely enjoy it.