A trio of cherries is usually suggested or 2 females. Most people want to have a male though since they are such a beautiful red color. In that case a trio is better so the male won't chase the same female all the time. I have 3 in my 29g and the male chases after both females quite often. With 2 of them, he won't stress one out.
They are great community fish and not nippy at all IME.