The risks of mixing more than one dwarf angel are serious... often they fight to the death. However, I love my flame and, even though some have had trouble with them nipping clams and corals, mine has been a model citizen. Bangaii cardinals are pretty cool to me also. I'd stay away from any more tangs... a 75 is, in the opinion of many, too small to house any but the smallest tangs (such as Tomini).
You will need a very mature 75 with lots of rock and a good pod population if that mandarin is to live.
I'd personally