How much coffee to add to American Imperial stout?

Tonight we're making wort for an american imperial stout... gunna hop it more than necessary with 3 oz. spread out over 60 min.

My buddy wants to add in some coffee. Is it a good idea to add it to the wort or should we wait till we're cooling the wort and mix it with water?

also, apparently the only coffee we have left has been sitting for most of today in the coffeepot while we went skiing. Is this going to be a possible infection problem?

how much should we add?

thanks!

Add some espresso after primary or at bottling

You skied today? Now I'm jealous...