Hi,
Your point about the topography is interesting and important. The typical height of topographic features, like ridges and refrozen rafts is about 100 meters (300 feet) maximum, which is consistent with thin ice (a few km thickness) as you noted. There are a few isolated uplift features that are a kilometer or so high. The ice is probably a bit thicker at those sites.
The main point of my book is not so much any particular thickness value for the ice, but that the ice is permeable, which allows direct linkages between the ocean and the surface. Those linkages explain what we see on the surface and also increase the likelihood that we will find life there.
I hope your readers will enjoy my new book Unmasking Europa. A more detailed version of the story is in the academic volume Europa, the Ocean Moon, also from Springer.
Richard Greenberg
Professor of Planetary Sciences
University of Arizona