In that case I'm still not sure about what depth means here. Is it the level of the house to which the Z elevation belongs or is it another thing?

Again, it's the depth of the virtual visitor in the plan, i.e. the depth of the following object when the Z height of the camera matches the eyes' elevation of a visitor with a human reasonable size:

So, if the "depth of field" lens is the NORMAL lens, how do I specify whether I want to use just the normal plain lens or the "depth of field" lens?

Use PINHOLE value for the Default lens and NORMAL value for the Depth of field lens.

So these values can only be changed at launch time and not by a pluging at runtime?

These values are used when the renderer is started (see PhotoRenderer class), and you can change them before launching the rendering process with the System#setProperty method.