There are a few different definitions of a 'splash' page. For example, one might want a page that will first display regardless of where the user tried to navigate on the site. Once they have viewed the splash page, they are free to browse as they wish. We don't currently support this type of splash page in glFusion.
But, my preferred way to implement a splash page is using a static page. There is an option under page format called Blank Page which basically means no header, footer, or navigation, just the contents of the static page is displayed. You could use this feature to implement a splash page.
For dual columns, the best bet right now is to implement this hack. Long term, I think it would be a great option to add to glFusion where you can select single or dual column layout for the main index page.