I had until recently 3 tangs in my 180 standard, a binotatus (blue eye kole)which I just lost to an internal parasite, a sailfin, and a mimic and all of them got along well. Both the yellow and kole are ideally sized for a 180 and several of the Acanthurus genus stay fairly small and like tampa reefer stated mixing different genus is usually a good strategy for success. I love my mimic, Acanthurus pyroferus, one of the three mimic tang species but I am not sure how it would get along with a yellow tang since most of the common mimic species are yellow as juveniles.
If this was my system I would add one of the smaller and mellower Acanthurus tangs like a convict or a mimic to the tangs you have already selected, and would add them in the following order; kole, Acanthurus species, yellow. Or perhaps add the yellow and Acanthurus at the same time.