H1 b approved in August 2013 still unemployed


I am in US from May 2012 on H4. I got my H1 approved in August 2013. But I have not started working till now. Will that be a problem for my visa.

Do I need to apply for COS from h4 to h1 or will it be done automatically once my h1B is approved.

How long can I be unemployed after my H 1 is approved.

Please let me know.