You may want to check here to see what characters are already taken and/or finished. Balthier is already taken, as is Bartz and Quina. In fact, both Bartz and Quina are already finished, although I'm not to happy with the Bartz one, so you can take a shot at him too if you like. The FF1 shopkeeper is not on the list, and is a bit too obscure and irrelevant for me to make room for him now. Marche and Black Waltz #3 are still available, though, so you can do them without any problems.