Hi Moniker,
Aside from your monthly salary, and perks such as air fare allowance and holiday travel allowance, it's perhaps of more importance to ascertain if the teaching assistance will be rendered as on teaching assistant to accompany you to each of your classes or the subject teacher of each class will act as your teaching assistant when you teach his (or her) class. The former arrangement is much the better one, for obvious reasons.
Your total employment package for 4 months of teaching should add up to 28,000 RMB for a teaching load of 16 classes/week; for 20/week, it shouldn't be < 32,000 RMB; for 22/week, it shouldn't be < 34,000 RMB.