Ctrl + Shift + N will create a new folder. I would like to use a different (2-key) shortcut.
I know I can use custom shortcuts, but what is the command to create a new folder?
There is no facility to customize keyboard shortcuts per user within Pantheon Files at present. If you feel a shortcut is inappropriate or missing in Pantheon Files you could raise a bug about it at https://bugs.launchpad.net/pantheon-files.
Note that some system keyboard shortcuts are customizable by going to System Settings/Keyboard.
Update: You could add a custom shortcut in Systems Settings/Keyboard that runs the command "pantheon-files -n". This launches pantheon-files in a new window.