But then again it depends how you care for your snakes. If your the shoe box, set the thermostat to one temp., and feed them once a week kinda snake keeper then they are different.
Green tree monitors are predominatly w/c and come in rough condition. This is something a new keeper to monitors should not start out with.
Your questions are very ballpark so to speak and not easily answered. if you narrow it down it would be easier. Example you asked how often do they eat. That can range from daily, mulitple times a day, 2 or 3 times a week, etc.. it depends on the situation at hand, age of monitor, type, etc..
Then you ask another one like how fast do they reach adult hood. That depends greatly upon the enviroment. In good conditions it will grow quickly in poor conditions it will grow slowly. Putting an exact number on its growth does not work either.
Read some general care sheets on monitors, then read up on the species your interested in. Search this forum your questions are answered within.
Good luck and if I were you i would start out with a different species to get your feet wet before jumping in head first.