Simple process for adding our own facades to our buildings in our downtown area? So far all I've seen is how to work with tutorial data and not how it was created.
To get facade data, you'll have to collect it from somewhere, whether you buy it from another source or take the photos of facades yourself or find another way to get a set of images. Depending on your images, you might need to process them, for example, to make the facades straight or crop out unwanted bits. Image processing software like Photoshop may be a solution, and CityEngine offers some basic cropping and alignment functionality. Right click on image -> Crop image. This opens a tool that lets you crop an image and fix the alignment so that things that should be horizontal are horizontal. This helps adjust an image with perspective (where horizontal lines are slanted), for example.
Then, as you mentioned, the tutorials and examples show how to use the facade images as textures.