Can I transfer my H1B to a company B before start working for company A?

I ahve Valid L1B till 2016. Applied for H1B transfer through a consultancy. Two weeks back I have received a hard copy of approval for my H1B petition for company A .

		Now my client (Company B) for which i am currently working want me to hire.
		So below are my concerns:
		1) What can I do in this situation with my [H1B]( approved? Can I transfer to another company on that petition even if I did not start working for company A?
		2) If yes, what are the main steps of that process? Does a new employer have to pay any additional fees if it wants to be my sponsor? How long is takes to have a new sponsorship approved?
		3) Do I have any deadline to find a new sponsor?
		4) What about salary and job description - do salary and responsibilities have to be the same as those mentioned in original application submitted by company A?