Can I resign from company after green card approval?

While your immigration status is involved, I believe this is more contract matter than immigration law, Immigration law wise, no one can force you to work. However, you may be violating contract term if you agreed to stay with the company until November, 2014. You really should consult with business attorney.

That depends, as your employment contract may prohibit you from doing so and subject to you substantial financial liability, which should be reviewed for such language by the local employment law attorney.

Don't stay home too long. Sometimes it is better to take leave travel, find new work and then resign after. When you still have a job it is easier to find another one. The new employer might wonder why there was so much urgency. Once you have a green card you are not tied to anyone - the 13th amendment prohibited indentured servitude. But this is (of course) the reason why companies don't see the benefit in sponsoring people for residence. Your green card means you are an immigrant. Your H1B meant you were a nonimmigrant. You can't be both. Good luck

I do not recommend quitting and departing the U.S. Consult with an immigration attorney to understand why.