L200.
Just get some plecos you like and see how things go. if all goes well, you can something else and if not... well, then you dont get more. its always hard to say how many cuz it depends on many things.
Depends on the pleco species of you want. It's obvious a 12" royal, 22" common, and a 6" bristlenose are going to take up more room and increase the bioload by different amounts.