Mini kits usually are simply that ... a small kit containing a sampling of papers and elements. Regular-sized kits typically have more papers and lots more elements to choose from.
Regarding downloading ... yes, you simply navigate to the file location on your PC and click the save button.
My advice is to have some sort of organizing system in mind. You'll be amazed at how quickly you accumulate digi supplies! Everyone has their own system, so you'll likely develop your own ... I'm just giving you a heads up to give it some thought.