Howard Miller

Firstly, there is no way to know how much time has been spent on anything. All you know is that a student has clicked on a video and downloaded it. They may have walked away while it is playing. You can't even tell that it is playing because it is playing on their PC not inside Moodle. This is nothing to do with Moodle, it's just the way the web works. To a greater or lesser degree, the same goes for everything else.

Grades are returned to the Gradebook in each course. There is no specific reports that will show the teacher data for students across multiple courses, although you may discover some workarounds. For example, exporting gradebook data in each course and organising it in a spreadsheet.

What you are looking for sounds sufficiently specific, that a custom report may be required to suit your needs. This will require development to be done yourselves or commissioned.

Yeh - my experiences with testing that plugin have not been particularly successful. It mostly works for simple cases but is easily confused.

Did you try (simply) re-enrolling them?

Yeh - if you installed Moodle and Wordpress so "close" together that this is is possible then the initial installation was badly planned. They should be completely separate. As Ken says, the redirects in Wordpress's htacess file can break Moodle.

No.

The Gradebook is a highly configurable tool for storing, manipulating and aggregating grades. One element is a "report" of the grades for students.