grrowler, I think the main issue is whether your partner shares the same enthusiasm as you do in living in a foreign land where English is not yet widely spoken in the local population. Without social contacts your partner may feel isolated and this can cause tensions within the family. Try and find some expat family in Tianjin (before you go) and spread out your network from there. This applies to any overseas posting, not just China.
Make sure your health insurance cover is adequate for your family's needs. Read the small print. Always have your medical card on the person, as most hospitals require a hefty cash deposit (even for ER) unless it is one which is affiliated with or recognises your insurance company.
Cost of living is low compared to Oz. Live where you are based. Commuting can be a touch and go affair due to frequent changes and cancellations in domestic flight schedules.
Oh, to add, only drink bottled water from reputable manufacturers and bought from the larger supermarket chains.