Have got the base upload form working. After uploading the file it's automatically creating placeholder records for all post formats (Wordpress' build in Post Kind),  Categories, and Post Kinds. 

But thinking more about the actual worflow, I think it will be better not automatically create those records and truly split it separate steps. So after uploading the file you're taken to a list page with a list of all uploaded Wordpress files.

Next to each filename there will be five buttons: "Set Category Mapping", "Set Post Format Mapping" ,  "Set Post Kind Mapping" (if found), "Import Media", and "Import Posts".  The "Import Posts" button will be disabled until mapping has been setup and media has been imported.

Uploading the file will automatically redirect you to the "Set Category  Mapping" page, but if you leave the process midway through you'll be able to pickup where you left off.

The base Wordpress import form