After much thought, I don't think Rolf is going to catch much pokemon. I'd like to create a dream team for him to strive for, but he doesn't really need a full team of friends and companions, because he's satisfied being alone at sea and unless something drastic happens he's not really wanting to be a coordinator/champion. He's never really liked them, unlike a lot of the others who love a pokemon in particular or grew up loving them, and he's more interested in learning about them than learning to take care of them. I don't know though, maybe that'll change as the story moves along.