L1 to H1 Transfer and delay in joining the date


I am currently working on L1B for company A and it is valid till Dec-2013 but i have proccessed my H1 with company B and it got approved and valid from Oct 1st.I have plans to go INDIA by this december so I am planning to work for company A on L1 until then and once i come back am planning to move company B.My questions are below,

1)Do i need to go for stamping in India?

2)I need to change the status of my H1 to inactive until i come back?If so whats the process?

3)Any issues in future?

4)I am valid to stay on L1 until its get over and then activate my H1 in Dec2013,would be a problem?

Please let me know.