Are you lifting heavy and sprinting? It's true that diet is the bigger factor in leanness, but if you're looking to build muscle, you'd probably benefit from 3 bodyweight/weightlifting workouts plus one sprint session per week, and maybe some long walks on your rest days.
ZC buggers fat loss in many people; the carb consumption = bodyfat guideline is oversimplified. Helpful for many beginners, mind you, but far from the whole story and not effective for everyone.
I think your proposal re 1g protein + 50g carbs + all else you need as fat is pretty sensible. Bear in mind that if you start working out, particularly doing heavly lifting, you're likely to need more food -- and that's FINE.