Atlus and parent company Index are aiming for 300,000 units sold for Catherine, CEO Yoshimi Ogawa revealed during an investors briefing that was held in Tokyo on the 14th. The game sold 250,000 units as of the end of February.
As expected, Catherine sold pretty well in Japan and I assume the same will happen, at least according to Atlus' expectations, in North America. But, from the beginning, I never would have expected Catherine to be the type of game that could be appropriately sequelized. I've not played the game (except for the demo) and I know practically nothing about its story outside of its initial premise, but I had the impression that the game's ending would not be the type that could lead to further adventures. Certainly, sequels would be totally different stories following totally different characters, so it could work. It would be weird to just have a game titled Catherine 2, especially if the game didn't even have actual Catherine in it.
As reported at Impress Watch, Ogawa said that she hopes to develop a variety of content business opportunities for Catherine, which she called Atlus' next new IP to follow Megami Tensei and Etrian Odyssey. She did not share specifics.