I just started one and im happy with my results so far. Id start with some hardy fish at first. clowns and damsels are easy. do you research and you should be fine. on a scale one to ten id say its a 3 with ten being the hardest. but it depends in what fish and corals you get. id suggest you visit dr. foster and smiths fish website at http://www.liveaquaria.com/
they give you alot of info on fish and corals and inverts. you can order all sorts of kinds of fish from them. you can call 1-800-344-3699 which is there number they can give you all shorts of advice.