I'll answer your earlier question first - a UV sterilizer is like a white plastic tube with a line coming into the middle of the tube and another line coming out of the end of the tube.  Water comes in the middle, and out the end.  While the water is flowing through, you have a UV light that zaps everything in that water column. 

IMO, you might want to wait and see what your tank is like & build up some experience with how things work out for you before spending a fair chunk of change on a UV sterilizer.  You might get one cheap from someone on the board who never uses theirs. 

I have one, but only use it for a week after introducing a new fish.  Having said that, I add corals ALL the time but hardly ever a new fish.  If you plan to have certain kinds of tangs, or if you think you're going to be stressing your fish out, or if you're going to buy fish that look only 98% healthy, you might want one.  Again, just my opinion.  I haven't had a tank for a year yet - - so I'm hoping you'll hear a few more opinions.