I would like to know the best type of fasteners to attach metal lath to exterior block wall.
Spacing? In the joints?
I will be applying cultured stone to it..

Thanks!

Not in the joints, right into the block. You can use a masonary nail, cut nail with a washer on it to pin down the lath. On cement we use a Remington 22c nail gun

I am facing an interior wall with stone. The house is made of 6 inch thick concrete/foam brick. Do I need to attach metal lath first? How would you recommend I do that?