1 and 2 are answered in the forums already. Links below.

As for 3,4,5 Carl is correct. We won't have integration into 2.1 in any deeper manner. If Meridian chooses to do something deeper in the future, we welcome it.. but we cant do deep support of Sooloos without the blessing and support of Meridian.

This might help you understand the database structure and how we deal with our metadata and your metadata:

Importing Content from Meridian Sooloos Systems

Leveraging Existing Metadata In Audio Files

Customizing Metadata

If this doesn't fully answer your questions, I suggest you post in the Roon forums, as our team will be very happy to answer your metadata questions.

Roon