It's quite quite active with monthly releases!

See here on ways you can contribute to Armory3D. Thank you for helping Armory3D grow!

Absolutely! The Armory3D Engine is licensed under zlib/libpng, which entitles you to sell your own game commercially if you wish to.

Note: Please be aware that the Armory3D add-on itself however, is licensed under its own licensing - Blender GPL licensing.

Please follow basic troubleshooting steps from here. If error(s) still persist, please open an ticket or ask for help at any of the Armory3D community platforms.

The Armory3D manual has a full list of logic node references. The references contain detailed descriptions of what each logic node is capable of and what features it comprises of.

To avoid bias, you"ll need to conclude that on your own. Here is a list of pros and cons of both game-engines that is maintained by the community. Feel free to open a pull request if you feel additional information could be added to the list.