The alimony and child support should be determined by your separation agreement. After the judge makes a judgment on your divorce decree and the saparation agreement, your hu*****and is bound to pay you the alimony and child support specified under the agreement. If he refuses to pay, you can petition to the court to enforce the agreement. Your hu*****and will have trouble if the court orders him to pay and he refuses.
Since you will move back to China, you may have difficulty enforcing the separation agreement. You may need a legal representative in US to help you deal with those issues.
I suggest you to retain a family lawyer, who can help you protect your rights.