The Affidavit of Support is the i-864 form. If you do not have a job that will continue when you move to USA, you list 0, and are relaying on the joint sponsor.
regarding 3 i would definitely list it as an alias on the DS-260. About 4, the medical exam will take place in China, so no need for an english translation. Typically at the NVC stage and Interview documents can be in English or the local language. It's only USCIS that required English.