blj1234
It's always a good idea to do a little homework on each fish. They do "look" interesting for sure .... but in addition to looking cool, many species have special diets and water quality requirements.
Some get along well with other fish and inverts, while other's will not.
Some species grow huge very fast, and others remain relatively small. You get the picture
Before making any hard decisions - I'd suggest either getting a couple good marine tank books, or hit the library, or better yet research them on the net.
If this 55 is your first tank - I'd hold off on the butterfly's and skip the seahorses.
Surfin Sam made an excellent point as well.
EDIT: you guys replied so fast there was only one reply when I started LOL -- all great advise.
( on work laptop now - Brian