Heya Tores, about the displacement: Indigo will subdivide the mesh where necessary on its own - maybe have a fiddle with the exporter settings for this to see if suits your needs?
That's a really cool church scene, I was just thinking of putting a dusty medium inside to produce those lovely "god rays"

You would need to make the glass actual glass with some thickness and absorption (using the new absorption layer transmittance feature to texture/colourise it), and sunlight to beam through. It will be slow to converge right now, but soon we will have architectural glass which will tremendously accelerate this.
Another thing to do to improve the convergence is to cover the window hole with an exit portal (for much improved sampling).