I suggest you don't bother making a special plugin. Instead, create a new course and store all your custom database queries there using the Configurable Reports plugin. You should also install the Generico filter, which supports SQL queries. In your course page, you can include links to the more complex individual reports.
If you want to create a simple dashboard-type page that gives an overview of a range of data, I believe the Generico filter will do quite a good job. Someone created a filter for a course dashboard on the Generico Showcase forum topic which gives a good idea of how it can be done, and there are lots of other ideas there too.
Creating Generico templates that incorporate SQL queries is quite tricky, as you also need to use JavaScript to display the data, but it can be done.