well, it is quite complicated, come in

usually people get OPT for one year after graduation and before H1B. I will suggest you get H1B, that will keep you safe for at least 6 yrs.

For green card, first step in I140 petition to immigrant. If you go through EB1 Outstanding reseracher or EB2-NIW(national interest waiver), you can directly file I140 with all the supporting materials, usually take you 6 months to prepare from scratch. And now it takes around another 6 month for CIS to approve your petition. if you will go through labor certificate, you will get the LC and then file a I140.

Before 10/1/05 people sometimes concurrent file I485 with I 140, now you cannot, you have to wait until visa number for I485 become current for people from China. Or you have to wait your prioity date become cureent, means the priority date reach the time you file I140. ONLY after you file I485 you will get the EAD (it is different from the OPT EAD).

So, for now, the only way for you to work is OPT and then H1B. Since you need to maintain your legal status before you file I485, you HAVE TO get it. Otherwise once your F1 expires, you have to leave US in a few weeks.