5500rmb in Beijing would be difficult to live on comfortably. This is the standard wage for public schools in china and along with a free apartment can afford you a comfortable life style outside of the major cities.

9000rmb and a free apartment is ok but again for a city like Beijing it's not what I would consider a top wage. As the dragonized poster mentioned you might also find yourself working very hard for that money both in terms of the number of hours a week you have to work as well the fact that it is teaching pre-school students which requires a lot of energy and is likely to be quite different from the experience and qualifications you both already have.

If it's an option then I would suggest living in a smaller city that has good transport connections. The new high speed train lines mean that it's very easy to travel around and see china's major cities without actually having to live in one.

As far as the general cost of living is concerned china generally offers the opportunity for either extreme. You can live on as little as 1000rmb a month or you splash out all your cash in a matter of hours. Most expats live somewhere in between. Things like going clubbing will certainly be at the upper end of the spectrum. Drinks inside a club in Beijing are just as expensive as in the west and at some clubs you will have to pay a cover charge or buy a certain amount of drinks to allowed to sit down at a table. Seeing as beer from a supermarket can be as cheap as 2rmb a can then the best thing to do is get pissed at home then go to the club just like you probably did back in your uni days.

Take your time. Interview with a few more places and don't be rushed into accepting a position you're not sure about.