Thanks so much for reaching out here! This is a fantastic question!
You are exactly right that you can use the custom landing page and add links for your applications. You can use either absolute / fully qualified links (i.e. https://www.example.com/app1) or absolute path-based links (i.e. /app1) in your href targets.
However, we would recommend moving that example directory out of the /opt/rstudio-connect directory, lest your changes be overwritten by a future upgrade to Connect.
Further, we would advise not to sink too much time into this process, as a coming RStudio Connect release should have a better story for creating these types of landing pages!!
(we are working on an improvement right now!).
I hope that helps! Please let us know if you have any further questions!