Filing N400 is it really necessary to send a copy of front and BACK of LPR card?

Yes.

I submited a I-129 fiance but my fiace can apply for a b2 visa to visit me and have her vacation without any problem.

She can always apply for one; but she is unlikely to get it considering her relationship with USC and immigrant intent.

L1B Visa with Expiry Date in Apr-2012 but I-94 is valid till Apr-2015. Should I file for L1B Extension?

I-94 determines the expiration of your status. Visa is a travel document. If you return to the U.S. after April 28, you need a valid visa in your...

Should I apply for differed action if I am married to a U.S citizen, or apply for residency?

I agree with my colleagues. You should go for the green card.

Can my husband/sponsor use his certificate of naturalization/US passport instead of birth certificate on AOS initial interview?

Yes.

What i have to fill for class of admission on i-131 re entry permit if i have permanent resident card ? (immigrant visa)

I agree with Hareon. Mention LPR and submit a copy of the green card along with your application.

Should I apply for H1B Consular processing in April and OPT for May to start in August?

With change of status the start date would be Oct 1 and you will be required to join your employer per the approved petition. Consular process...

What do i write in g-325a form my husband sent me about my father's name being ask there?

I agree with Morgan. You will provide the name since you know it. I do not believe there will be too many questions raised whether he was your...

Can I travel on my J-1 visa if the process has started for the h-1b visa?

If the employer is seeking a change of status, and you leave, the COS is abandoned. Talk to the company's immigration attorney for guidance.

I agree with my colleague. If the company's immigration attorney has not already provided you with the list, visit the Consulate's website and...