Portability questions during year 8th/9th/10th

[schu]

I worked for Employer One on a H1B, during which also applied for GC (EB3) and I received an approved I-140 (priority date 2008 Feb). During my employment I received H1B Extension for my 7th year, and another Extension for my 8th/9th/10th year (2010 Oct - 2014 Sept). The wait was too long though, so I changed my employment to Employer Two in 2012 Jan, and USCIS processed my H1B Transfer, and now I have an approved 3-year Extension with Employer Two (2012 Jan - 2015 Jan).

My current employer (Employer Two) is wrapping up the first part of applying my GC (EB2 this time), i.e. placing ads and interviewing candidates, etc., and is about to (but not yet) submit paperwork for the PERM process.

I now am looking to a potential Employer Three transfer. My questions are:

1. Am I allowed to transfer my H1B Extension from Employer-Two to Employer-Three, using a still approved I-140 from Employer-One?
   
2. While working for Employer-Two, I travelled out of the country and has a visa stamp valid with my employer's name on it (valid till the end of my H1B extension). If I were to in the future work for Employer-Three, will my next travel require me to re-apply my visa stamp from my home country? Or my visa stamp is valid till the term specified, regardless of my employer's name so long as I maintain my status in the US?
   
3. Does my future Employer-Three need to sponsor me for a new GC process immediately after I start?
   
4. Let's say I join Employer-Three, and they do not (immediately) start my GC process. Then down the road, my priority date from my Employer-One sponsored (and approved) I-140 becomes current. Assuming that Employer-One is not interested in revoking my I-140, would I be eligible to apply for Adjustment of Status (without Employer-One's help), even though I no longer work for Employer-One? What is my risk in this case, such as can Employer-One revoke it before/after 180-days of me applying for Adjustment of Status?
   
5. How will my job description/nature difference at the beginning of my employment with Employer-One (non-managerial) and Employer-Three (managerial) matter, if at all, in the above scenario?
   

​Thank you very, very much.