It is very slow growing indeed, so you will be able to prune it without any difficulty whatsoever, say, once every few months, even in a heavily dosed tank. Corys won't bother plants, except perhaps uprooting the odd new one, if it's tiny and delicate. I wouldn't be so sure about the Plec, it could knock it around a bit, and for all I know, the plec could eat your moss.