a sump is never a bad thing. it increases overall water volume which helps keep the system stable, along with being a place to hide your heater(s), protein skimmer, and whatever else you plan to use. it's not a must however, and i've seen nice looking reef tanks without sumps. it's up to you. i personally, do not like the look of a HOB
skimmer hanging on the side/back of the tank. i'd rather have it hidden.
sterilizers have their place, but i don't think they are necessary in this situation. They kill whatever goes through them, good and bad. it's not going to protect against disease, or stop algae problems. i'm with those that consider it a needless expense.