Yes! Once you buy it, you will have access to all the future updates of the addon.
Yes! You may download the free demo (including the plugin) from our website
The library is prepared and optimized for Blender Cycles. Most of the objects (non-glass) should work perfectly with Eevee. You may use it with other software after converting the models and the materials to the desired formats. Maybe in the future, we will work on the library's conversion to other formats