You download all kits to %appdata%/kits
That is not acceptable (or even standard), you should at least give the user the option to choose the data folder, since the room on c: may be sparse. Nearly all artists I know have dedicated data drives for these resources. Another option could be to delete the kits after the program is closed, but I see the advantage in cacheing them. So a user-selectable data folder is the preferred solution.