i suggest the same as the others, blennies, gobies, clowns, maybe a wrasse...are you going to have corals?
And yes, almost every tang requires a 6 foot tank. There are a few others that dont like kole tangs and tomini's they can do well in a 75g or bigger though
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.