Thanks for trying out the QuickStart!
To use the repositories in RSPM from the QuickStart, you can navigate to the "Setup" page for a given repository to view the repository URL that you should use in the RStudio IDE packages configuration dialog:
You will see that you should add /latest to the end of your repository URL, so that it becomes:
http://localhost:5000/packages/curated-cran/latest
which behaves as a valid CRAN repository.
Or in the case of other repositories such as the CRAN mirror, you can choose either the latest package (e.g., http://localhost:5000/packages/curated-cran/latest) or a fixed set of packages from a particular checkpoint/date (e.g., http://localhost:5000/packages/cran/151).