I think you could do all four.. but since you are talking about adding new livestock I will assume this is a new tank.. so my response pertains to that situation. I would..
1. eel then wait a month.. snow's are hardy
2. lion let it claim its space in the tank.
3. wrasse It will quickly learn to leave the lion alone..
4. trigger I would get a picasso instead of a huma. I think if you add it last it will do good and not be agressive.. my picasso is scared of my hippo tang because he know's his place..

plus picasso's look better.. IMO..
but again there is no right way to do it.. you know fish have itsy bitsy brains.. but they have HUGE ego's and attitudes... thats why I think all fish are female..

JUST KIDDING.. god I see the tomatoes flying already..