The tank looks really nice!! Other people have posted about braiding nylon ropes with plants in it ( mostly types of moss ), I wondered if that would work since it doesn't need the substrate. Maybe the Angels would enjoy the rope if they like the upper levels of the tank.
My sister had a red tailed shark in her tank and it was incredibly aggressive and would pick on the other fish, though I do not recall if it actually killed the fish. If you have a quarantine tank you might want to be prepared to remove the red tail have a small basket to cover him with upon introduction into the tank, until you see how he is going to be with the other fish.