All right, since I didn't want you to give up, I tried myself on some 'solidary shadow creation suffering'.
As the supposedly "real" shadows (according to sketchup + lightup - similar to Frito's rendering) turned out to
look rather aweful in this isometric view (as in "not real"), I went with a combination of real and stylized ones
(...after "some" try-outs). (Apparently I had too much free time this weekend
Unfortunately I got rather carried away, overdid it somewhat and
in the course, ended up butchering your scene kind of:
As Snarky and Frito already mentioned, simple and stylized shadows are easier to do and fit nicer into
the scence (...it reminds me a bit of 'Little Big Adventure', they had 'stylized' shadows under their sprites as well)
It really doesn't matter how bright the light bulb is, and how far the light would travel in "reality", it's
really more important that it creates a coherent mood in your scene.
Playing around with your scene, I also realized that the wing chair is rather too big for those couches. Since the wing chair
looks good in this size, I'd recommend enlarging those couches & the table somewhat.
Also, in order to make those crisp & hard shadows not stand out so much, I'd recommend putting highlights where the light hits
the furnitures. Tried this with the large couch in a really quick and messy way (- not a very good example!).
If you would brighten the left side of the wing chair (from our point of view) for example, it would make the wing chairs shadow
instantly more pleasing to the eye
Other than that, lovely scene!