If you get the BN and get rid of the common pleco, you'll get good. Watch out for the angelfish pairing off. I would be worried about 55gal (4ft of tank) not being quite big enough for two full-grown pairs of angels since they can get pretty territorial. Also, black skirt tetras are notorious fin-nippers, so keep an eye on your angels fins. I would actually up the number of tetras to eight or so to keep them occupied with each other and then they'll leave the other fish alone. Also, when you get the BN pleco, make sure you have driftwood in the tank to supplement his diet (if you don't already have driftwood in your tank).