When designing a template, proceed top down. Building a template is like building a house: Start with the building, then furnish the rooms; only put the pictures on the wall when all the furniture is in place.
Don’t hesitate to make scribbles on paper. Often, scribbles on paper inspire creativity much better than designing on screen. This is especially true during the early stages, for example, when developing the general layout of the type area, or when designing the title page.