There is a very informative post about the asset and all of its features on the Unity Forums.
There are a number of different ways you can recieve support, but the easiest and recommened way is to join the discord channel.
The asset currently costs $30. The price will gradually increase as it is further developed, but if you purchase it now you will recieve free updates.
The asset was released on the Unity Asset Store on May 22nd of 2018.
Currently it does not, it is optimized to work with a fixed size world. However, support for infinite terrain is coming in future updates.
All block data is stored in memory for efficiency, there is no dynamic reading from file. This means the max size of any world is just over 2 billion blocks, however the actual amount of blocks your system can handle will depend on the amount of ram you have. Although, I already have an updating working engine with infinite terrain which will be released in coming updates.
Any suggestions for additional features will be taken into account, but in the end I will have the final decision of which features I wish to add to the engine.
I have not done extensive testing on mobile devices or web in the current version of the asset, although I don't believe there is any reason it should not.
If you still have any additional questions you can contact me here.