I don't need to worry about the gratuity part yet, but as a consumer, let me tell you how I feel about "added" on tips. If you add any amount to my bill as an automatic tip then that is all I'm going to tip. Nothing else. If you let me add it on based on how well I like the service, then chances are you are going to do better than whatever it was you were going to add.
That being said, I know there is risk there for you and your staff. I think you have to feel the customer out when it comes to this. If you think they are going to stiff your staff, then add it on. If you think they might be more generous, then risk it.
Now I have a question for you. When it comes to the gratuity? Is this for just your staff or for you and your staff. I've never considered "me" getting a tip.
EDITED ADD ON:
The food looks really good. How long did it take you to wrap all the asparagus? Great job...