Main focus? Dude, um... as far as main focuses go, I'm pretty sure Riku wasn't really one of them. He was big when it came to plot twists (and true, he DID have his own plot in CoM), but...
Oh, and Arica, I don't know if there ARE any confirmed shots of Riku, but I think it's safe to assume he'll be in KH2. Personally, I hope we see some pics of him soon -- he had the most interesting character development in KH, and the ending of CoM made me eager to see where he'll turn up next.