Visa details for UK passport holders living in Ireland

Hello,
My wife and I are interested in traveling to China together and teaching English there for about 6 months, but possibly for 7 or 8 months, from August 2011. Is it best to apply for a 6 month visa and then, if we decide to try to stay longer, to apply locally for an extension visa, or should we apply for a longer visa at the start, just in case? If we want to work as English teachers in China do we need to get a special working visa?

We both have UK passports but have lived in the republic of Ireland for 30 years. Can we apply for a visa through Dublin? What documents would you require please? We don't have any special forms authorizing us to work here, as they are not needed.

On some of the forms I think I read that we must buy return flights before we can obtain our visas. How would this work if we wish to return by train via Moscow? Can we buy a single flight to get to China and then later buy our train ticket in China for the return journey?
Thank you