Generally people will say no tangs in a tank shorter than 6 foot. It isn't water volume, its distance available for swimming as they swim a lot in the wild. The yellow eye kole tang might do ok a for a while in a 40 gallon breeder. Many will comment on how you need a tank that can accomdate the fish for its lifetime - so starting with a small tank isn't a great move.
This all said, I'm sure there are people who have sucessfully kept a variety of different types of tanks that were undersized. However, a 40g breeder is def. undersized for most tangs. I'd stick with the kole tang idea or think of something else.
If you are looking for a show fish - something more impressive, a coral beauty or a flame angel might be better choices. But then again a small kole tang would likely be happy.
On another note, I have a 55 gallon and find it frusturating as really all you can keep are fish that could be happy in a 40 or in a 30 long, or a nuvo 38, -> basically large nano tank sized fish. I think you need to step up to 75 gallons to be able to start thinking about larger tank fish. And 75, frusturatingly again, is likely the minium. Still, to my wife's disbelief, a small tank.