Also, the Copyright attribution field is set to required. Had to enter something there to export an addon.

Additionally, the version defaults to 1.0 yet all the other addons are 10. Is this version for the addon or the version of Composr it is compatible with? Maybe would be nice to have a field for both.

Fixed the bug.

Made it a drop-down as suggested.

Copyright should be required. Even if you're giving it for free, it's still copyright based on some license.

Version is for addon. By convention we default the bundled addons to the same version as Composr, but for non-bundled it's typical to start at 1.0.
I've clarified the description.

Addons may be compatible with multiple Composr versions, so I wouldn't want to code that direct into the addon archive. I can see why it might be good, to give a compatibility warning, but normally they'll be distributed through the addon directory anyway.