The password for your account or for the q&a posts? Though both should have let you make your own password. You should be able to change your account password, but it's stuck as-is on the message board after you post. I think most forums are that way with password protected posts.
If paypal shows your payment complete there's probably no problem. I've never used paypal for them, so it may just be an issue with how paypal reports back to their site.
You'll probably get a reply from them by tomorrow. I find the companies tend not to do correspondence on the weekends. I'm not sure where you're located, but you might look up the time difference between you and Seoul to get an idea of when you may get a response. It's almost 24 hours difference from where I'm located, so I know that I'm more likely to hear from doll companies in the evening or night than during the day.