L1 to H1 visa transfer

I am currently on L1 (from A) and in US and will be filling for H1 (from B) in April 2015.

Questions :-

  1. When will the change of status be filed? Let’s say if its filed in month M, then can I travel outside US from M 2015 to Oct 2015?

  2. I believe, if everything goes well then H1 start date will be Oct 1, 2015 and on that day I should be joining B. Please confirm. Do I need to do anything here?

  3. Should it be applied for change of status or normal h1b sponsorship? What are pros/cons?