Yes, OnGetNodeHeight can be used to scale manually. The Icon is not stretched, this is currently not an option unfortunately. We'll investigate if we can improve this here.
Sorry, this is not possible. You'll need to add a smaller image directly to the bitmapcontainer to make sure the image is smaller. Additionally, the OnNodeGetHeight is called when the node is being calculated. After it is calculated the event is not triggered anymore. When the text changes, the OnNodeGetHeight event is retriggered. The Height of the node is a global height, which includes icon, text, etc...