As long as the cichlids keep their aggression towards other cichlids the poly should be fine (and with 30-40 doesn't sound like it should be a problem). One thing I would worry about is the bichir getting enough food. I would monitor these next couple feedings and see how much food he is getting so that if he is not getting enough you can spot it sooner rather than later.
I am hoping he can grab a little one every once in a while, they are all over the place and often right in front of him. Including babies its probably 50 plus now that i think about it. Its hard to judge because of the extensive rock formations. I was planning on supplementing him with worms