I've been drinking decaf from the day I got home from the hospital. I let it cool a bit and add a scoop of choc. Jay Robb to get some of my protein in. 26 gm a scoop and nice mocha flavor.
Coffee could be a diuretic to some people. Those of us who are heavy coffee drinkers it usually does not. Our body has already adjusted to the coffee and no longer acts as a diuretic. There is a study out that supports this. It depends on you and your physiology.
I drink boatloads of coffee everyday....full on Starbucks with added espresso shots (or two). I also make sure to drink 80-100 oz of water a day, though.