I want to get a visa to China

Good morning

I am Palestinian, a resident in Brazil - Sao Paulo, I have a number (RNE) in Brazil, and I own identity / residence card in Brazil, I studied University and lived in China for several years, went to there more than once (twice + exit and entry, from / to China).
I studied there, in universities (Beijing, Nanjing, Shanghai, and Jinan).
I own a Palestinian passport (issued by the Palestine), and I have special travel document to the Palestinians living in Syria (issued by Syria).
I have a number (RNE) in Brazil, and I own identity / residence card in Brazil.
I would like to obtain an entry permit in order to visit PRC (I want to visit there, do not visit one of the persons / no specific person).

What documents are required?
Can I get a entry permit for more than 3 months?
Can I get one for 12 months?
How long will it take to get? And how much does it cost?
I do not know exactly when I will go there, but I'm planning to go in the spring (March)..

Thank you