You MUST save your PlayOnline password to log in with a SquareEnix account. They just don't let you save the SquareEnix password for security reasons, and in case you are using a security token, since it's input on the same screen.

The resolutions are individually for the window size, menu overlay, and 3D environment prerendering before it is stretched/shrunk to fit the window.

I understand creating a new account is quite different than it used to be, and as my account is from JP game launch, I don't know all the details of using it. However, I've found little trouble actually using any of the menus if I actually stopped to read them.

The Steam install does hide the configuration programs used to set up the game, so installing from a disc is better, and I keep a copy of the disc on my hard drive to speed up installs when I get a new system.

The current system is a major improvement over the old billing and registration system though. You should look up how it used to work.