Daz import is done through the Collada file format. You export from D/S in Collada, and import that Collada file in Vue.
And yes, you need to install Vue 7 to get an installation code, so you can register it at e-on's. Once it's done, you can upgrade to Vue 8 from e-on's site, and then buy modules for Vue 8 at Cornucopia.
If you decide to buy Vue 8 Complete, there will be no need for modules, they are all included in Complete.
You'll still need to buy SkinVue, though.