Buy Agricultural land

I can help you with 1 & 2 (from my own experience).  My example is identical to yours - wife from farmer family, I am not from one.

1. Can my wife still buy an agri land, even after her marriage into a non-farmer family?

Yes, my wife could buy.

2. Can I also be added to the purchase deed as a 2nd owner? If yes, do I need to get any special permission?

In our case we were not allowed, my name had to be removed from the sale deed.  In fact we had purchased stamps in my name, we could not use those stamps and had to pay stamp duty separately in my wife's name.  However, I was later told by several people that I should have been allowed as a 2nd owner.  However, once the sub-registrar refused, we did not insist.