Re #1: Glad to hear that it is on your To-Do list.
Re #2: Yes, my database schema does have foreign keys that point to non-primary key columns. It is a reasonably sophisticated, but coherent, design that is described in a paper you can download from here:
where you can find diagrams of the database schema and explanations in the text. If you'd like me to beta-test the next build of OpenAccess ORM that is supposed to be able to handle these kinds of associations, I'll be happy to do that for you.
Re #4: I hope that you will consider making the names more clear to prevent confusion, and I will continue to suggest "Database Schema Explorer" versus "Conceptual Model Explorer" or at least something that clearly contrasts the "Database Schema" from the "Conceptual Model". Another alternative would be "Database Schema Explorer" versus "Conceptual Domain Explorer" so that there is no use of the word "model" at all and then there's no confusion about which model the term "model" refers to.