Rendering

For rendering I used V-Ray.  I turned on indirect illumination and set Primary bounces to Irradiance map (with medium settings for test, and high for final image) and then Light Cache for secondary bounces (with subdivision of 200 for test and 500 for final image). With the final settings, it took about 5 hours to render the final resolution of 4000 x 2000pixels.

Post-production

I always work on all of my pictures after rendering in Photoshop.  This is so I can paint out mistakes and play with contrast and colour correction.  I took a few hours painting in some small details with a 1-3 pixel crisp brush, and adding some blur and shadow adjustments.  With your picture, it depends on personal taste, but always have your pre-painted and current image loaded in so that you can compare them and see what is working best.

Oh, and don't forget the background for the image!  This can be done easily by saving your rendered image with an alpha (tif or targa file format), and then using that as a selection in Photoshop.  Now, place your desired (or painted) image in the lowest layer, and it will only appear through the "hole" in your image (like a window in a room, for example)

Conclusion

I hope this has helped you out: remember to research extensively, and don't be afraid to experiment and spend extra time in post-production.  Many great images do not come just from the 3d package; they are a combination of work from many different mediums, including your concept drawing.