VISA Restamping while I-140/I-485 in progress

[Rashan]

I need some advice based on your experiences/knowledge about my situation - any help will be greatly appreciated.

My situation is:
- I was employee of XYZ India Pvt Ltd with L1-A petition stamped till Dec-2019 working continuously in US since Mar-2015.
- This month I got transferred over to parent company XYZ Corp in US so that they can file my green card, in that process my L1-A petition got transferred over from XYZ India Pvt Ltd to XYZ Corp with newly approved I-797 having petitioner name as XYZ Corp and validity till Sep-2020.
- I-140 and I-485 are not yet filed and XYZ Corp may initiate that as soon as I give them a go ahead

My need is: I need to visit India two times in next 6 months, in Dec-2018 and Mar-2019.

My questions are:
1. Do I need to re-stamp the VISA even if I have earlier stamp for old I-797 valid till Dec-2019 (I think yes but anyone through this situation and did not re-stamp while visiting to India)?
2. If I need to re-stamp then is it advisable to wait till Apr-2019 to file I-140? Any impact on re-stamping or I-140 if it is filed and either in progress or approved by Dec-2018?
3. If I need to re-stamp then is it advisable to wait till Apr-2019 to file I-485 (assuming I-140 approved in premium category)? Any impact of re-stamping or I-485 case when I go for re-stamp?