Bichirs are slow to get to food, since they find it by smell. I'd feed the other fish first, then drop in stuff to the bichir. Some use long tubes to get food to the bottom past the midwater fish. You could also feed them after lights out, but I like to watch my fish eat.
A BN pleco should be fine with the bichir - even though some plecos will suck the slime coat, the general consensus is that BNs specifically are generally OK. Watch for problems of course...
