QUESTION : Do you have the toolbars and menus I posted above?
Make sure you have the latest 3.4 version of V-Ray for Rhino. Then, make V-Ray the active renderer. If you don’t see the toolbars (or menus) … then solve that problem first.
I didn’t make much use of the studio floors from Express and haven’t looked for them in v3. As Dave points out, the infinite plane is there but it isn’t quite the same. I tend to just model something if I need a specific background.