This is similar dimensions to a 20 gallon long. About 30" long and foot high and wide.
It is too small for a tang, unless it is a baby and you have a home for it once it starts to grow up. The mandain is pushing it, unless you are feeding it manually it won't last long. Likewise with the chromis, one might do okay, but two won't last long. I feel like it is not enough space for a blenny either...
I'd stick to a couple clowns and gobies in a tank this size, like a fire fish, watchman and a clown. A couple neon gobies might be good too!