Well, there's ten of them, and while it's just Twilight (and probably Cheerilee) for the demo, there will be more girls in a future final build. So at least five more, maybe ten more, hell if we're feeling extremely ambitious, twenty is probably a maximum amount possible.
So that means we may need 50 of these in the final game, probably closer to 100 of them, and VERY UNLIKELY up to 200 of them. With these numbers in mind, honestly just write however much you feel is comfortable. The way the game is built I can basically load in as many text boxes as you need.