A theme is derived from a template.
So if you converted the home page template to a theme and applied that theme to the other pages, then yes, your other pages would use the same design as the home page.
a Theme is only need to be used on pages where you want to apply a consistent design.
The content that is unique to the p[ages is defined in editable regions.
When you create a template, you add editable regions to it. whatever is no in the editable regions is applied to the page as the design. on each page, you add the unique content into the editable regions.