They are much less popular than Hanshin Tigers and I personally doubt they will sell out this game but it is the penultimate game of the year, so I will leave that judgement call to those on the ground.

As for the website, it's not terribly difficult to click through to purchase tickets but my worry is that they will not accept non-Japan based cards. Obviously, I don't want to try with my credit card but for these sorts of things. When prompted for contact information, I've found that putting in the hotel's address and contact information usually works, ie when I did the JAL hangar tour earlier this year but I don't know if that would be sufficient when charging a credit card (the JAL hangar tour was free).