Hi,
> I want to use the same basic project with the same variables throughout all my projects.
Project as a whole cannot be used within another project.
Project variables cannot be shared between different projects.
You may add existing project as a whole to as many test suites as you like.
Also, you may add components (script units, keyword tests, etc.) of one project to another project(s) via the 'Add | Existing Item...' context menu functionality.
You may consider to use Project Suite variables to have their values to be accessible for all projects within this given project suite.