Coffee is very good. Your decision to keep it black is very wise. NPC's have no clue how many calories they get from things they add to their coffee, so I can only laugh at normies when they whine about how hard it is to lose weight.
Coffee has positives and negatives. Its a cheap way to get a large boost of antioxidants and add in a thermogenic effect, but the freeform caffeine shocks the adrenal glands making them weak over time. Good in moderation but not good for the long term in high amounts. Just don't add sugar to it, which basically turns it into a heavy soda.