4. Constructor vs. OnShown. In the Type Safe Builders, you don't have access to all the screen geometry that is being prepared and will be realized long (in computer terms) after the Scene Graph is built. Almost all of my initialization appears in OnShown. That gives me the opportunity to put in progress bars. The Stage methods like init() were once used when combined with a preloader, but I haven't seen this in a number of years.
Putting stuff in the constructor or builders may delay the showing of the window.