Integrate multiple forms as optional steps in one form

Context

I'm working on a CMS portal that supports content in a set of categories. The categories important for this questions are in particular;

  • Media
  • Pages

When adding media, the users has to complete a form containing the following fields in a one page form;

  • media
  • title
  • description (optional)
  • tags (optional)

The problem

The problem I'm facing is that pages also can contain media. Users can add existing media from a list, but also add new media right there from the add-page-form.

I'm struggling to find a good flow of doing so. I've thought of a few ways so far which all have some pros and cons;

  • 'Add media' is a button in the form that shows a dialog with the add-media-form;

The form is quite long to put in a dialog. This is also inconsistent with other forms.

  • 'add media' is a button that takes the user to a second page in the form;

I'm not sure if having a multi-page-form is good UX. Especially since the user will return to page one upon completing the add-media-form-page.

  • add the add-media-form to the add-page-form in the same page;

This will increase the form length significantly. It's also problematic since it's quite a long form for an optional step.

  • allow drag-and-drop/click-to-upload media without the add-media-form.

This way users can upload media without the required fields which will just make a mess.

Question

What is the best way to integrate multiple forms as optional steps in one form?

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