Rainbows can be aggressive and peaceful at times. They will stay to them-self (As in being peaceful) If you give the appropriate size tank (At least a 55 gallon, 75 gallon preferably; In your case, you shouldnt worry about it), Enough hiding spots/ territory (Plants, caves, decor), and the right tank-mates -> Nothing too aggressive (Im sure the shark could fend for its own though) or able to eat them.
I would also recommend getting a small bottom feeder such as Cories (Panda, Bronze, peppered, albino) or a Bubblebee catfish.
Once algae starts configuring in your tank (and you can start supplying algae; Wafers should do fine), you could consider adding a bristle nose pleco or two
How about a pearl gouarmi? They are great 'bigger' peaceful fish.
Do you have a breeding plan for when these angels pair up?