I hold a LLB from the UK and intend to sit for the NY bar exam. I am not attending any course but will self-study. My question is:

1) Is it necessary to learn the American cases in each topic?

2) Both legal systems are based in common law but apparently the developments from common law have been quite different. Does it actually mean that I have to learn the subjects all over again?

3) Any experience to share?

Thanks.

1) Yes.
2) We have statutes and a written constitution, too. Very little of the law is common law.

My recommendation would be for you to sign up with a Bar Review provider like BarBri or Pieper -- its your safest bet to pass the first time around!