Page Type VS Custom Tables

Custom table (or custom module class) is good for storing large amount of data, however you can't use workflows/versioning with it. So if workflow is a requirement - go with page type, or you'll have to implement custom workflow for custom table.

If you need your white papers to be in the tree and be part of the url, use page types. I have over 500,000 page types and in Kentico 10 there is no performance degradation.

Adding items to the content tree will help with SEO, navigation, search and so on without any additional coding. If you have these items in a custom table or a module class, then you need to write additional code to get the SEO, navigation and search abilities. Some are easier than others but out of the box you won't get ALL the features as you would if you placed them in the content tree.

Page Types will be better in your case as it helps in many out of box features

You can use event handlers for Publish after in work flow and on published after event handler we have move the page from content to custom tables. In this we can use workflow and save document in custom tables.