Will I be able to retain my initial Priority Date when my new employer files for PERM and I 140

[WorriedConsultant]

I am in the 4th year of my H1B visa, my I140 was approved on November 15th, 2016. My employer is a staffing/consulting firm. They had assured me when I was joining them that they never revoke I140 even if employees switch jobs. 
We have got my spouse H4 EAD on basis for that. 
I want to start looking for direct employers now for more stability. If I switch jobs now : 
1) Will I be able to retain my initial Priority Date i.e. July 12th 2016 when my new employer files for PERM and I140 
2) Will it have any impact on my husband's H4 EAD. 
3) Do I need to wait for 6 months after the I140 was approved before switching jobs to retain my initial PD. (remember reading this somewhere) 

Please advise.