Hi,
I'll try to answer your questions.
1. There's no one unique way to integrate DBXL with Sharepoint. There are a few options, depending on whether you want users to be able to delete, for example. This document is a good start, but there are more options that we are in the process of documenting.
2. No. Only SQL and SQL Express.
3. In the software's web.config you can define administrators who can set up mapping. You can also define Readers and Writers.
Feel free to email sales at qdabra dot com for more info, a demo or anything else. Thanks!