Designs created in Mail Studio behave pretty much the same way as regular emails do if images are disabled. You should add alt text to your images and plan your design so that a missing graphic doesn't cause problems. Still, we're at version 1.0 so I imagine we can do more about this.
The app handles the HTML part of the email, while the plaintext is entered by the user when preparing their campaign. We won't be of much help there.
As a suggestion, you might consider recommending where missing alt text is, especially on call to action buttons, and perhaps providing a preview of what the email looks like with remote images disabled.
Good mail providers will block remote images by default, and that's a trend I'd expect to become more prevalent over time.
The app handles the HTML part of the email, while the plaintext is entered by the user when preparing their campaign. We won't be of much help there.