How does Divorce affect our residency?

Divorce will not affect your immigrant status.

If I want to study in university may I enter with o1 visa and changed it to student after one year?

As long as you intend to keep to the terms of the O visa when you enter.

Can i get a green card by marrying a US citizen?

If she files an immigrant visa petition for you, you can file to adjust your status. You need to file certain applications with the immigration...

After i obtain a immigrant visa can i use it to obtain o job meanwhile im waiting for my greencard

Once you enter the U.S. on an immigrant visa, you already are a permanent resident and you are allowed to work.

My father adjusted his status in 2005 through Nacara section 203 based on an asylum application filed before April, 1990.

NACARA is not asylum, so if your father were granted NACARA you don't qualify as an asylee, but you may qualify as the child of a NACARA applicant.

Which forms should I submit for Affidavit of Support for family based green card application ?

If your wife's income alone is sufficient there is no need to file an I-864A.

How long does national visa center takes to send me my immigrant visa after my i601 form has been approved

About 3 weeks.

File a FOIA to get a copy of it. No fee. If you have other proof of lawful entry, you don't need the I-94.

Can they obtain residency without returning to Mexico?

Living in the U.S. alone is not a basis for residency. Rather, generally a person immigrates to the U.S. based on an immigrant visa. This may be...

Applied for reinstatement in Dec, 2011 and havent heard anything from them yet.

If you have finished your courses, I don't see any advantage to deciding not to graduate. That won't put you back in status. If you graduate you...