I-90 timeline and QS re travel

[mig42 0]

I had my appointment for my I-90 to change the name on my green card on March 25th and was fingerprinted and photographed.

I'm just wondering how long it will take for me to get my new card back with my married name on it?

(I applied in Newark NJ if it makes a difference)

Also,

I'm due to fly to Ireland in June/July but I don't want to book my tickets yet as I don't know which name to book under. So a few qs for you..

(1) If I book under my maiden name but my new card arrives before I leave will I have a problem getting back into the US with my old green card? Also, I'm goin for 6 weeks so what if the card arrives while I'm over in Ireland? I guess what I'm asking is, will my old card expire at the exact time my new card is sent out or is there a grace period where you can use the 2?

(2) I need to renew my driver's licence before June 30th but need to show the MVC that I am still legal in the US... if my new green card doesn't arrive by then I don't know how to prove that to them. Has anyone ever been able to get a letter from USCIS to say their application is being processed? Or has anyone else been in this situation before?