Hey Chris. If these will be in your 180 I think they should fine. I would put the possum in a little while before the six line. You may rarley see the possum wrasse as they seem to hide quite a bit, IME. The six line is one of my favs. They are always out checking out the live rock and other fish. I have had some pick at feather duster type worms though.
Andy
I have an 80 gallon with lots of live rock and caves, have both a 6 line and possum in it, they get along fine. the possum is more shy then the 6 line, he only comes out during feeding. otherwise they get along fine