H1B transfer without pay stubs


I am in L1 visa with employer A, I have applied for H1 with employer B (A consulting firm) and got my visa approved. The following are my questions,

  1. I have not received any visa documents from employer B. What visa documents I should have as a proof that I have H1B?

  2. What docs I need for visa transfer if I am moving out of employer B after few months?

  3. Can I directly join a new employer C by transferring my visa from B to C? Is it legal? Can I join a new employer C without any pay stubs from employer B(Without working for B even a day)?