Transfer of WP queries

[LondonGuy]

Hi

I have few questions on Transfer of Work permit.

I am working for Company A on WP and got a job with Company B who is ready to sponsor my WP.

1.After getting the WP approval for company B, How long can I work for company A?
2.After getting the WP approval for company B, can I start working for company B after serving notice period of Company A without getting the FLR(ID) stamped?
3.How much time I have to get the FLR (ID) stamped for the company B?
4.If FLR (ID) is not stamped for company B, can I go out of UK based on the FLR (ID) stamped for company A and come back to UK?
5.Does anybody know whether it may be possible that my FLR (ID) can be rejected for company B? Should I start job with company B after getting the FLR (ID) stamped?

If anybody can share his experience of WP transfer and let me know when I should resign from the current job as I am really scared if there is any problem. Please help me out.

Thanks