The official Spring Festival Holiday might last for one week or 10 days, whereas you might not be teaching for four weeks or longer! Chinese staff at public schols are paid for the whole of the school holidays, but you're in the private sector.
Ask about currency conversion. It might be you are restricted to only being allowed to convert 30 percent of your monthly salary to foreign currency, but by the month, not at the end of the contract!
Ask if your salary is gross or net. Income tax will likely be applied, so maybe gross.
Can't think of anything else, good luck!