Best to to change from H4 to F1


I am on a H4 visa and I got admission in a good university for Fall 2014. I got the option to join as an in-state student which is way cheaper than studying on F1. Hence I chose this option. But I eventually want to  go to F1 visa so that i can utilize the OPT option.


1.  When would be the best time to apply for change in status considering OPT is a top priority.


2. How long should I be on F1  to get OPT.


3. If I change from H4 to F1 midway through the Masters, would I still need to take 9 credits per semester to maintain F1 status?


Please suggest.