- Is it possible to group different versions of a file together?
No (although you can create a special category for each software).
Is it possible to add tags? Is it possible to search for tags?
Depends what you mean. There's nothing that stands for "keywords", but everything that you write in the file's details in searchable.
- It would make sense if the super-category could see everything in the sub-categories....Is this possible?
Not...from - I mean, for - a Jedi. Unofficially I guess it's possible to hack it.
- If I want to re-structure my categories at a later date, can I do so without losing all the uploads?
Of course. Each file has its unique ID anyway.
Can I set certain groups to be able to upload without approval?
Yes, give them via Geeklog the permission "filemgmt.edit" (please correct me if more filemgmt.X permissions are needed beyond what a registered user gets by default).
But they have to upload through the admin menu.