Clarifications on Green Card adjustment

[RavindranSS]

hi - GC was filed in 2017 in Eb3 category. Now, the employer is trying to adjust to EB1. I wanted some clarifications with regards to this process:

1. How will the dates be adjusted when the category changes to EB1 since original filing was in 2017? Will EB1 dates also move back to 2017 and what would processing times look like to get the GC?

2. Can we travel for outside the country when this process is happening?

3. If we continue with EB3 and move back to India, what needs to be done to retain the GC processing / port the dates if we change employers? 

4. What are the residency requirements for a GC? I have known folks to keep visiting every year for few weeks / months until they are ready to settle down...pls advise.

Thanks for your help!