You can divorce your F-1 husband and marry to the U.S. citizen.

No, but if you have to disclose the info in your I-485 application, specifically, page 3, part 3 C, question 1 if you ever smoked marijuana.

Does time spent studying abroad disrupts continuous residency status and is cause for denial?

I can only answer your citizenship question. You have to be in the U.S. at least one half of the time necessary to satisfy the naturalization...

No.

L2 to H1 visa

1. You will become H-1B from 10/1. Yes. Your H-1N have to be consulate process. You need to leave the U.S. after your L2 status expires on May...

I was on H1B visa till August 2011. After that I went out of the country and reentered on H4 visa,dependent to my husband's H1B.

Hi, It will be a change of status application, and you will not be subject to the H-1B cap.

Immigration question

I think that is doable.

Can you reduce work hours of a us worker while PERM was filed for H1 B worker in similar position.

Yes.

Question regarding G-325A and the box at the very bottom of the page; "Applicant: Print your name and Alien Registration..."

You fill out your G325A, and your wife fill out her G325A.

Can dependent on F2 visa legally work in US?

No.