Can i reentry the U.S with my i512?

Not good idea . You might be inadmissible for 10 years.

It takes about four-five months. You are almost there.

I have a job offer out side the USA.

You have to preserve your status in U.S. see an attorney to discuss your situation .

Can I get married if I have J1 with 2 years requirment and 16 y.o. and apply for K1 or K3 with a person who is 17?

Check state law to see if you can get marriages while under age. You need to see an attorney who can by looking at your documents say if you have...

INS 101 Where to start ? Filing process Mexican deportee later married to Mother of children. Wife US BORN Citizen. 7 children

You need to talk to an attorney to see what inadmissibily issues you have and what waivers are available .

Will it still take 10+ years for my US citizen brother to petition me for legal status/permanent residency.

Yes, he can. Not really.

What to do if my US passport is taken from me by a US consulate abroad?

Nothing to do with immigration.

Refile

Can I live in the US if I get married to a green card holder?

The approval of your spouse petition may take about eight month. If you are not in the U.S. you would need to wait for the visa to become current ....

My i-485 was filled with my i -140 ( alien of extraordinary ability filed by employer.

USCIS shall adjudicate your case soon after receiving your employer's answer to RFE.