Convict are probably the easiest Cichlid to keep. The females are idetifiable by their red color on the stomach. The males are typically a little bigger with longer fins(not always), and no red on the stomach. They will eat any fish food you give them flakes, pellets, blood worm etc...lettuce is not really going to do much for Cons.
As for breeding them the male will protect the fry along with the female. Both parents will bring food to them so feeding is not an issue. Typically the like to spawn in a cave. A flower pot works great for this. Young convicts may take take 1 or 2 tries before they are successful. The first couple batches sometimes go unfertilized or are eaten.
The male will tend to be aggressive towards the female. As long as they are at least an inch 1/2 they should be ready to breed.
Give it a few months and you will have baby Convicts. And soon after that you won't want them to breed any more.