Changing styles for type would have no effect on the page layout. The columns and gutter settings are set per page, so may or may not be relevant (they will fit inside the established margins).
The panel menu is accessed by clicking ther little icon in the upper right corner of the Pages panel.
You might find it just as easy, or maybe even easier to set up a new document to use as a template. You can import your styles from any existing document by opening one of the styles panels (Paragraph or Character), and opeing the panel menu, then choosing Load Styles...