How to decide content for text boxes
The content of a text box is decided by applying merge code to the text box, e.g [FileSize]. In the given example content from the file relating to file size flows into the box. You can mix static data (data not surrounded by [ and ]) with variable data (data surrounded by [ and ]).
Can I apply character and paragraph formatting?
Yes, the way you use InDesigns built-in features to format text, is the way your module will appear in production (WYSIWYG).
All you have to do is define paragraph or character formats.