Dropbox_I797 Current Employer Vs New Employer

[Raygad]

Guys, please advise me.
I am mechanical engineer. This is my 2nd H1B extension. Current employer A approved 797 validity is Aug 2019 to Aug 2022 (Visa stamp expired Aug.2019).
I received offer from employer B and transfer will be premium processing. I will have approved I797 with employer B prior to my vacation.

1. Dropbox on new employer B I797 before joining employer B? (Any risk) so far I never had any RFE or denial.
2. Dropbox on current employer A I797 and join the employer B after coming back
3. Dropbox on new employer B I797, Join the employer B for a week and go for vacation (employer is agree with the vacation)

Appreciate your advise