12" is really pushing it for Aquaria. They'll grow to 8" in a few years, 10" in larger tanks in a lifetime. Largest I've ever had and seen was 8". In numbers they are probably the most aggressive Ace. but nowhere near as aggressive as Cichlids - just nippy with smaller fish or amongst themselves. Cohabing cudas isn't really about how much of a threat the cuba is as to how much of a threat the other fish are to the cudas. They mix well all kinds of non-aggressive fish of similar size, small fish that can fit in their mouths will get eaten.