[TLDR] 4 ounces coarse in a pint jar for 24 hours - filter and add to bottling bucket or keg for 5 gallons [/TLDR]
I'd start with 6-8 ounces of coarse ground coffee in a quart jar and fill with cool water. Shake it up and let it steep for 24 hours then strain. Cheesecloth filtering before you pour it through a coffee filter will help considerably, but be prepared for it to drain really slowly through the coffee filter.
If you want to dial in the coffee presence in your finished brew i would add about 1/3 of the coffee to the fermenter, swirl it up very gently to mix, and then let it sit a day or two to blend and settle. Taste it, and if you like it proceed to bottling. If you want more coffee flavor, add more and either wait again, or bottle it and cross your fingers.
This is all easier if you're kegging. Just transfer to the keg, add 1/3 of the coffee, and carb it on up. After a few days you will have a good idea of the taste, and you can always open the keg and add more coffee if you need it.
-Ben