That should be fine. It could live out the rest of its life comfortably in a 40 breeder, but the 55 is ideal. In my experience rainbow sharks are less aggressive than redtails, but can still have an attitude. Your BA tetras are hardy fellows though so they should get along with him just fine.
55 gallon Planted Tank - 10 gallon Reef - 5.5 Pea Puffer
2015 AA Fantasy Football Champion