Hasn't AYS been there for quite a lot of time? I doubt it's one of the brothels the police are hugely bothered about, more interested in the people trafficking or neighbour complaints causing kind of brothels I would have imagined. But yes visiting a brothel is technically illegal, this is true, it's never a way of punting which has no risk attached to it...
Anyway, to answer the OP, I wouldn't really bother with booking in advance or extras at AYS. It's a cheap and cheerful pump and dump kind of place. So, I mean, you could always phone up on the day before visiting to ask who is there on that day and just go if the girl you are interested in is in on that day. It's not like if they are with a punter when you arrive that'll you'll have to wait long for them to be done with that guy and available.