Besides the tank not being big enough for the oscar it is probably too small for that many angels. I will at times stock angels like that, but I have plenty of extra tank space at my disposal. If you have this option great, if not you are overstocked. Not knowing the species of plec it is too small if they are common plecs. Some of the others may grow too large, many do not. My oscar took out a 14" common plec,
The oscar will eat the mollys, and nip the angels to no end. My oscar took out a 14" common plec.
Oscars are smart, busy, and in many ways devious fish, they like to mess with things for fun. If you want an oscar get a larger tank, and expect the oscar to rearrange decorations to it's liking, break heaters, remove filter intakes, break thermometers, toss spray bars out of the tank, a whole list of fun things. It's like an aquatic toddler rum amok.