The 3 different Kontakts are stereo, 8 outputs and 16 outputs, you can see this when you actually look at the dlls.
So they each have their own uses depending on how many outputs you require.
As to hiding plugins not being used in the plugin menu there is a selection of 2 check boxes that allow to enable and disable plugins. It can be reversed if you later decide to include it again.
As far as A DX version of Kontakt i don't remember there being one. Unless there was an option to install a DX version of Kontakt and you said yes.