The OP's issue is that his current passport expires before the initial flight. And as TG ask for passport number and expiry date when booking, presumably their system would not be able to proceed to completion.
Indeed the case. I would always say getting the non-O in your home country is better, it eliminates the need for a trip to immigration for one thing, and the minor airline issue.
As is widely reported these days, opening an account without a non-O is nigh on impossible. However, getting a non-O in your home country is easy. Doing that you make opening a bank account easy and avoid airline issues with onward tickets.
Indeed. But a lot of individual consumers, myself included, were migrated to K-Biz when they shut down K-Cyber Banking. Those that like to use a web based interface rather than phone app will still be using it.