First, convert all materials to iRay base.  There is a built-in script for G2F and G2M that can get you to a starting point.
The other scene materials you will have to do manually.

Next, you should decide whether scene is indoor or outdoor.  If outdoor, in render settings "Environment" select "Dome and Scene" or "Sun-Sky Only".  
If indoor, select "Scene Only" and you can use just the photometric lights and/or use the Emission shader to make your own light objects.