The reason i didn't want to get more angelfish is if a pair forms , they would tear up the black ghost knife when in breeding mode. the rocket gars seem pretty skitish, probably to skitish for a tank in the dining room
ABF look really cool but spend a little too much time floating motionless for my liking. Remember that they're jumpers so make sure your tank is well covered.
Another option to consider is a school of larger tetras, eg. congo tetras or colombian tetras. These species should be large enough not to be snacked on by your BGK and would add a lot of activity to the tank. I'm not sure if fin nipping would be a concern with the angel.