Uhh. Steven, Lance, Gary, and Wallace? These people seem to gather a lot of fangirls. -personally doesn't care much for Lance or Wallace- x_x;
I suggest that you keep the amount of characters to a minimum. Maybe... eight at the /very/ most? I mean, it'll already be confusing enough for the players to navigate through all those characters, but you'd also be designing the game for thirty odd characters. Wouldn't that be tiring? The most I've seen for is around fifteen characters, including two secret ones (Seirei Gakuen, for GBA). But if you're up for it, I won't stop you.
And, I think keeping Pokemon in the game would be nice. You could have most of the game in sprites, mainly have the trainer catch Pokemon. Maybe catching certain Pokemon or talking to people at a certain time of day could trigger CG events? ...This'll be making the game even more complicated. Bother. Anyway, I don't think basing the entire game completely on a dating sim is a good idea.
Good luck on making it!