The Privacy policy will be seen in your app’s listing on the marketplace. If you look at any of the currently published apps on the marketplace you will see their privacy policy. We do inspect it during the app review process to confirm it satisfies out requirements too.
In the Information section of creating the app, under Links > Add Your App, I have selected From your landing page and not From Marketplace.
In this case, I assumed the app would not be available on the Marketplace and therefore would not be available for users to see via the Marketplace. Is this assumption correct?
The Installation method doesn’t have anything to do with that the difference is the landing page will direct them to the direct landing url you set and the from marketplace will allow them to install it from the marketplace that’s all. Once you apply for publishing your app will be listed on the marketplace.