When you set up the 55, you're going to want to put the plants in before the fish, so the plants can get their root system going. Fish can be pretty hard on some plants. Any ideas for what type of plants you want? Plantgeek.net is a good place to find the plants you like.
I don't think that the butterflies will bother the leaf fish too much. I've heard that leaf fish hide in the plants a lot, so they probably won't be at the top much.
Oh, and one last thing (for now, at least). If you do happen to fall in love with the bichirs (it happens to the best of us!) you could always get rid of the South American fish and stick with the African fish. Just an idea.