Sometimes it is helpful to use the Joomla! debugging system.
For example one category could list Downloads by date but another Category could list them in alphabetical order.
How to create large number of downloads automatically.
Using an Akeeba backup to make a local test site with Wamp
Using Joomla Debug mode to Show permissons for all categories and downloads graphically by user group.
Customise jDownloads front end with jdownloads_custom.css