Red tailed black shark
Although the red tailed black shark is a great looking fish, I really would discourage you from adding one to that tank.
Reasons being that you clearly have a very pregnant balloon Molly, congrats on that I hope all goes well, which is a relatively slow moving fish. You also have gouramis and also angelfish. Both the gouramis and the Molly would have a hard time dealing with the aggression of the mature red tailed shark because they are slow. The shark is also notorious for fin nipping, and it would really be a shame for the angelfish to become victims of that.