The advantage of agent tabs is that you can define a single tab that gets re-used for a lot of similar things - in Pathfinder, all classes use an agent tab, so that they can use the same thing, but at the very beginning of HL, in d20, you needed to define a separate tab for each class.
This page of the wiki describes the parameters allowed on tables:
http://hlkitwiki.wolflair.com/index.php5?title=TableDynamic_Element_(Data)
Allowing the user to sort it is the allowuserorder parameter, and to remove the space allocated for the scrollbar, set scrollable="no". Your component will also need to be set up with an orderfield to allow that to be added multiple times.
Whether an item is unique or not (and can be added more than once) is controlled on the individual items, not on the table.