All metadata that is extracted from images is stored in the table gs_MediaObjectMetadata. You can construct a SQL statement that updates the Seq column in gs_MediaObject based on the desired metadata item. It will be a little tricky since the date is extracted as a string and stored as a string, so you'll have to convert it to a date in your SQL statement to get true date sorting.

Yes, although that is not a requirement. You can give it any number, and the sorting will work because sorting is done by relative comparison of Seq values.

Gallery objects (which include media objects and albums) are sorted by the Sequence property of the GalleryObject class. That is, the implementation of the IComparable interface in GalleryObject uses the Sequence property to compare itself to other instances of the same type. This implementation is used by the .NET Framework when the Sort method of the GalleryObjectCollection class is invoked. The sort method is called within Album.GetChildGalleryObjects().

Hope this helps,