At this line, in response to an update touch event, I go through all the children of a named node, remove some and add others. The key is that the node I am adding and removing the nodes to is identified via an fx:id tag in the FXML:
I already use SceneBuilder but I don't know that create controller with him.
For bound, I don't speak about binding but more specific boundsInLocal for a Node. I already read the API doc here (Node API Ddoc), unfortunatably I don't understand very well this concept. Just help me to understand this with your word it's good (I don't remember what way in your code let me here but I want to understand nonetheless).
Generally you don't need to worry about the layout method in JavaFX, unless you are writing a layout manager. I've done quite a bit of JavaFX and have yet to need to figure that one out.
I speak about your code Controller class and more specific siezScrollCircles method.
Example : scrollEnd.layout();
Thank for your binaries distribution. Just pity that for gesture concept (good idea however).