Applying for spouse's H4 COS during my H1-B Transfer

I have exhausted 6-years of my H1-B visa and I have,

An approved I-140 from employer A that I left 2 years agoand currently working for employer B on H1-Band recently got approved for H1-B transfer to employer C, where I will be working in 10 days from now.Due to issues at my wife’s work place, we are trying to apply for H4 for her (she is on H1-B).

Should I wait until I join employer C and get a paystub to file for her H4? Or can I just file with employer B’s H1-B and paystubs?Would traveling to India and getting H4 at the US-consulate be the best option for her to change status to H4? The approved H1-B for employer C got renewed for 3 more years so I am assuming the I-140 from employer A is still active, correct? If so, can I use that to file for my wife’s H4-EAD ?Any help is really very much appreciated, thank you.