I would only recommend 2 orchids Dottybacks, not 3. One male and a female. The tails look completely different between the two - so if the tails look alike, don't get both. Two males or two females will fight. I've read that the orchid is about the most peaceful of the dottybacks, but two of the same sex in a 55g is asking for trouble.
Looked at the yellow eyed Kole tang? One of the smaller ones and a bristletooth variety that can help keep algae mowed on the rocks. Let's see what others may say about that in a 55g.
"Life may not be the party we hoped for but while we are here we might as well dance!"