V-Ray will get very close to a real world situation regarding rendering, but everything is designed to be visually equivalent and not numeric or Data driven.
The main issue for you is exposure, because any light analysis system doesn't take in consideration, because it is not relevant for illumination data.
If you need to get "exact numbers" and values. I would recommend using any light analysis software/plugin that is around, you can find them in all flavors, for REVIT, Rhino, ArchiCAD even for Sketchup.
3D Max has a light analysis overlay, that is kind of useful but t was designed to work with Mental Ray, I am not sure if this works with Arnold or V-Ray.
The way you describing preparing the materials sound good to me, but again I would not trust V-Ray or Arnold to do a correct Light analysis. Light analysis software are designed to do that, and have many other settings and features than V-Ray or any other image rendering tool can't give you.
