in addition to ChilDawg, your angel should be ok with your rtbs, I have kept them together for a few years now without a spar between the two. The rtbs will most likely find a corner or cave in the tank and claim it as his own and be most focused on that. The only problem you'd have is if you got another rtbs (or something similar, such as rainbow sharks) and tried to put it in with them. The rtbs can be a bit territorial once he's staked claim somewhere, but never has there been a problem with my angel swimming too close to his cave.
in addition (just saw your new note) those balas are going to be a big problem quickly, they can get quite skittish and will be evident to you shortly in that size of tank. I would return them as soon as you can (whenever you can) and go with the store credit......sooner or later, you will see, you will use it.