I have a sheet where I have all my projects and then sub categories indented underneath it. Is there a way I can easily add a new project that will create automatically add the sub categories?
No, at least not inherently within Smartsheets. To circumvent this we keep a template at the top of our sheets that we can copy to create new "projects." You would just have a blank project with no dates and all the durations and dependencies set up. Then you can just highlight and copy the rows to create a new project.