One solution I would suggest is to go to the line that error is happening and remove the line of code where the row that is trying to be added is failing. This may be a bug on our end that slipped past us in development. Otherwise, I would advise against using dummy data as if you plan to use the app in the future, without using MySQL the dummy data will be hard to remove later on.
Edit: This actually is fixed in the newest release, we will be updating the Github soon.
Yes, that is correct. This is because we develop using SASS, which we then compile into the CSS files that you see in layout.css. If you want to make edits, I would suggest copy and pasting the CSS files into a CSS prettifier.
The other option would be to install compass onto your instance, make your changes on the SASS files in compass/, then running compass compile from the compass directory. This will compile your SASS files and generate new CSS files in themes/ (of course after backing up your project files)