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Lots of ways to do ribs, but I go with a lower temperature to start 240-260 and it holds steady through the entire cook. That would be my suggestion, but you will get many different opinions when it comes to the best way to cook ribs.
To some of your other questions, I have added coal on long cooks, but if near the end, I sometimes just wrap in foil and finish in the oven, but just depends how close I am to desired temperature as to whether it makes sense to add more lump or not.
I havent ever used water in the Egg, have never seen a need for it, and most people on here seem to agree.