EB2 is possible
EB2 Green Card
Your lawyers are right in that CA is not accepted as education by USCIS. Speak with a credentials evaluation agency about Master's degrees.
You COULD qualify for EB-2 depending upon your qualifications and the job requirements. If you leave before I-140 is approved, you may get nothing out of the process. But leaving after I-140 approval gets you your priority date to carry forward.
It is possible and common for employer B to get H-1 extension based upon an I-140 approval of employer A. You need to speak about the details with a lawyer.
You need to speak with your lawyers to decide on the timing of the filing. For EB-2 a requirement of minimum Master's degree or in the alternative Bach. + 5 years of post bach experience qualifies you for an EB-2.
Depends. If the SE diploma is post graduate (not available for undergrads) AND recognized - you MAY be eligible for EB-2.
If your BS and MS are in the same field and are related to your work, EB-2 should work.
Theoretically, this is possible. As to the practical implications, you must speak with the lawyers who will represent you in the second green card process.
Yes, you qualify for EB-2, unless the alternate requirements, if any, for the job are less than Bachelor's + 5 years exp.