H1-B transfer before stamping and while traveling outside the US


My H-1B stamping is in three weeks and I have received an offer for a new role which I want to accept. I am currently outside the US for visa stamping using my current employer’s petition. A decision on the petition that my new employer will file will likely not be made until after my currently scheduled appointment. I will be traveling back to the US at the end of January. How should I go about the change of employer?
1. Can the new employer submit an H-1B transfer petition to USCIS before I have the visa stamped using my currently approved petition?
2. Can they file it while I am outside the country?
3. If my new petition is approved before my return to the US, will it cause any issues at the point of entry or could I enter using the visa stamp with my current employer? I will not be resigning from my current role before returning to the US.
4. Does approval of a new petition automatically invalidate the original petition or can I continue employment with my current employer until they officially withdraw it? If it’s the latter, it would mean I will have 2 approved petitions with two employers for a few weeks.
5. Is there anything else I haven’t considered? Looking for some advice regarding the right chronology of events.

Thank you for the assistance!

I answered your post on another forum, please check.

Thank you! @Kalpesh_Dalwadi