So, is the SHIELD authentication process available via an API? This will allow me to have a single-sign-on for the user into their web-page and Kibana authentication behind the scenes automatically.
There is an API for adding users and roles in Shield 5.0. Single sign-on is pretty common with users of Shield. Usually it's accomplished either using run-as or building a custom realm. Feel free to ask a question in the Shield channel about your specific SSO scenario and how these two options may apply.
For each user's dashboard, it will be auto-created for them. Do you have a link with a sample/tutorial for auto-creating visualization and added it to a new dashboard and saving the dashboard?
I don't believe there is such a tutorial. You can use Sense or even Kibana directly to examine the contents of the .kibana index prior to determining the best way for you to write directly to it. Feel free to ask another question if you try doing it and run anything specific that doesn't make sense.