Angels are a single or 4+ group kind of fish. Many people have kept them solo and many people who have tried to keep them solo are disappointed in their personalities. I personally believe angels personalities shine far brighter in groups of four or more, but they can be kept solo with no health issues as a result.
Having said that, I am growing out about 20 1-1.5" Philly blue angels in a 55 all their own. I am going to pick my four favorites and add them to my 125 and pick another 6 and keep them in the 55 with a group of 8 sterbai cories.
I would also remove the idea of the bichirs unless you intend to move them to a larger home. The species of bichir you are talking about can grow to 18" and will be very cramped in that 55. Two of them would take up a massive amount of space on the bottom.
There is nothing wrong with housing bichirs and angels together. It is highly unlikely they will interact at all, much less have aggression issues. So if you want to upgrade the tank to at least a 90 for one bichir or a 125 for two bichirs, you could house the rainbows and some angels. A 90 would hold about 4 of each while a 125 would hold 6 of each.
Now if you don't plan on an upgrade, I would pass on the bichirs. Their size is just too much for that tank and they add a very large amount of waste to the bioload. Instead, I would plan for a school of 8-12 Cory catfish with 4 angels and some schooling tetras of a medium body (like lemon tetras, bleeding hearts, black skirts, etc).
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