I'd be honest about the fact that you are going to be there only for a year. As you quite rightly mention, this prevents any thoughts of you becoming a long term boy friend and also prevents the girl from getting hurt if you suddenly mentioned it a month before you left the country!
In terms of advice for you, I'd just say be yourself and you'll do fine! As you've probably already discovered:
# Your unique in terms of looks.
# You have the confidence to approach girls and chat to them (which puts you ahead of 95% of the resident population!).
# Your from overseas which should give you loads of credit as Chinese girls love guys who've travelled, even if it's only to a few countries!
# You have an interest in their culture, which will earn you a lot of kudos.
In terms of a few specific tips:
# Don't go to one area time after time to do day game. This isn't Oxford Street or Times Square, where no one will notice what your doing. The fact that you stand out will mean that you'll be noticed and to keep going to the same place to approach girls, will possibly get you some unwanted attention. Try and go to at least five or six places. You mentioned an approach on the metro, which is good. Shops, markets etc..all provide oppertunities. The old daygame classic of asking what to buy/how to cook line works well in these places (field tested!
Indirect openers such as directional/situational/opinion work well as a lot of girls may be overwhelmed by a foreign guy comming up to them, to compliment them, so by just starting a conversation, you can still build comfort and attraction with the girl.
Kareoke is masively popular in China and quite cheap, so if you have a half decent voice, it's a great idea for a D2 (and a quiet place for isolation
Have fun and keep us posted!
P.S. As for the Sugar Daddy issue you mentioned, it's a sad fact that for many poor Chinese girls an older rich guy is the only ticket out of a life of poverty. I've seen it in Russia as well, and you've only got to go to Thailand and see the number of old British guys with young girls, to know it's not only China. Try and ignore it and bring some fun and happiness to girls because of who you are and not how much cash you have in your wallet!