Really depends on if your gonna make it a reef tank or a Fish Only With
live rock tank.
As far as I know, most butterfly fish (aside from the copperband i think) and trigger fish are NOT reef safe, meaning they will eat coral and/or inverts.
as for the lionfish, you could do that if you kept it with one or two other fish around the same size.
Tangs need A LOT of swimming room and the only tank that is really suitable for a 55 gallon is the Yellow tang, but even that is pushing it.
I'm currently in the process of setting up a 57 gal reef tank, so stocking options for me are very similar to you.
It has taken me a LONG time to figure out what I want in my tank, and I'm still not even sure about my stocking list so far. And I have been planning for like 2+ months and havent even put any saltwater in the tank yet (Although tomorrow I am hopefully going out to buy about 30-35 gallons of water to put in the tank and the rest later on in the week.)