Oh ok. So the friendship bar can be 0 as long as it is existent and is in the relationship panel.
Not entirely sure. Having more friends (and higher relationships) may boost the chances, but...idk. Normally, my sims don't have enough time to establish close relationships, so my guess is that you technically don't need it. But it may boost your chances.
But really, if you don't like the result, you can always save beforehand and just reset if you didn't like the results (assuming it's not a challenge kind of game/file/whatever).