You can create cards and layouts before you have content, but unless there's content to back them you won't see anything useful on the device.
What I do if I'm interested in just stubbing out a few articles to prototype the structure of an app and play with cards/layouts is I'll create banners instead of articles. Banners are quick to create and don't need a .article file, yet still behave like articles for the purposes of cards/layouts. You can even have them point to an URL so you can get a bit of a feel for what content would look like by pointing to existing stuff on the web.
Once I'm happy with the prototype I'll delete the banners and replace them with the real .article content for the app.
Neil
