Well, if you are planning on keeping certain species of fish long term you have to take more than bio load into consideration. I totally understand that you do not plan on breeding angels. Your angels do not understand this, and there is no way I know of to make them understand this.
You, being the more intelligent species, have to take this into consideration. There will be certain unavoidable behavior traits when they mature, I'm trying to tell you the best way to have angels that are compatible with each other, as well as the other fish you are keeping. Territorial aggression, pairing, and spawning are things that are well within the realm of possibilities when you are keeping angels, unless you keep one single angel in the tank by itself, with no other angels. Fish will not behave a certain way just because you want them to, though it would be nice if they did.
With 4 angels you have an 87.5% chance of a pair, meaning there will be two odd fish out. The mathematical probabilities are unavoidable, they are the same for any unsexed species. The problem with angels is that you can not determine sex 100% unless they are actively spawning.
Much like dogs of a certain breed, fish of a certain species may be more or less aggressive depending on the individual. You may have a group of five that grow to adulthood, and have no pairing or aggression issues, but the odds are against it, 4 fish, 3, 2, it doesn't matter.
Unless you see some aesthetic value in angels that are missing half their fins this does have to be taken into consideration. If you want it totally hassle free, with no aggression or territory issues, keep only one angel. Any more than that and you will more than likely have some aggression issues in half of a 55.
The platys/molly won't bother any of the other fish, I keep corys with angels in nearly every tank, they are good tankmates, as long as you keep the temperature towards the low end for angels. Angels do like it warmer, 78F+. 78F is towards the top end for most corys.
Sorry it doesn't get any easier with angels, they are going to be the sort of fish that they are going to be.