I was reading up on the game and saw that it claimed that there were 10 classes, but only 9 character slots (6 free, with the ability to purchase up to 3 more). That seemed rather dumb, especially given that Korean imports usually seem to be good about letting you have ample character slots. So I downloaded the game to check, and now it allows up to 11 character slots: 7 free, with the ability to purchase up to 4 more.
That makes a lot more sense, as it lets you have one more character than there is class. At launch, it was a cap of 9 slots for 8 classes, so still one more slot than class. Presumably they'll increase the max number of slots available by 1 in the future whenever they release a new class, though it's very possible that at least some of those increases will require you to buy the extra slot if you want it.
I haven't actually played the game yet. I just thought I'd report that for the sake of anyone who likes to play alts and was wondering but didn't want to go through the entire download just to find out.