my firend has a pair of red devil ( in yellow color) the male he has was like 20cm and the female arround 10 cm. But my friend was force to seperate them for a while after breeding. You can give it a try usually 10cm should be enought to start breeding. But just watch out tho if u see the male constanly attacking the female seperate them.
(American/English) The one's that I had were 4 inches, and they had about 125 babies.
And the interesting thing was, only two were bought, and they both so happened to be a female and a male. And they also grew very fast...
But trust me, you do not want them to breed, especially if they're in a tank with tons of mates. For them being 4 inches long, they both kicked the Pacu and the Oscar around...