I don't think that catnip is bad for kittens. I heard that most don't respond to it until after 6 months. Also, some cats have no reaction to catnip.
Clyde also loves bells. You can buy them at most craft stores and add them on toys yourself. Just make sure that they are secure and kitty plays with them under your careful watch (you don't want him to swallow it). He also likes those mice, especially the felt ones or the ones that make a quiet "shaker" noise.
Any suggestions on a horizontal scratching surface? Clyde doesn't use his post but loves the carpet. I don't care too much now, because we rent, but when we buy it will be an issue.
ALSO - I have seen scratching posts that wrap around the corner of walls (or door frames). Maybe that will help with the climbing..