1. Any PNG/SVG output you make using the app, using its default library are free for use in both personal and commercial purposes. You are not required to credit the app or us, so it's kinda like CC0.
2. It's not available even in the full version (for now). It's planned for later date (remember, this app is still in development and hasn't even reached version 1.0 yet)
3. Yes, but for now, not yet.
4. Currently you can't add your own parts, but it's already planned and the feature will be there when version 1.0 is out. But please remember that when you use custom library items made by some other people, our 'basically CC0' license might not apply.
Thanks for your interest!