When we apply for H4 COS, Is F-1 CPT valid till the time COS is approved?

If you maintain F1 status, yes, it will be valid.

Can I add my husband to my EB3 petition if he was previously out of status on G1 visa but has left the US?

I believe you can, but I also think he might have different issues coming back. Consult with an attorney.

How much time does it take for H4 COS & EAD to get approved? Is it ~3months for H4 and additional ~3 months for EAD?

Not it is not additional 3 months. The processing times are published on USCIS website. But in reality times vary.

Withdrawn Asylum and EB2 Application

Let's say that your asylum application was not frivolous, however, the questions still be: how you will be able to adjust status from "status" that...

H-1 to H-4 COS, H-4 EAD and H-1B extension issues

I believe that USCIS gives H4 only from the date when the extend, one year starts. (So the basis for extension matter). Consult with your attorney.

It is your personal decision if you should change your name or not. If you do, you will need to present your marriage certificate showing the name...

Is it legal stay while waiting for OPT appeal?

If you win your MTR, you will be "legal", but if you don't , you will be "illegal". Follow up with USCIS. Make an infopass appointment.

WITHDREW WIFE'S PETITION ON 10/14/2015 DUE TO SOME ISSUES IN OUR MARRIAGE CAN PETITION STILL BE SALVAGED, LETTER WAS SENT NVC.

You might have to restart the process.

Bio metrics without Appointment notices - I485 EB1 Employer Green Card

It is possible to come in on a different date, but in your situation, if you do not have notices at all, I do not believe you will be accepted.

SENT LETTER OF WITHDRAWAL ON 10/14/2015 TO NVC. BUT CHANGED MIND CAN WIFE'S PETITION STILL BE VALID ?????

It all depends. You should try contacting NVC and ask them to disregard the letter. I believe the content of the letter matters as well..