As one of Vuo's developers, I work on Vuo's engine (the thing that makes compositions run), work on nodes, and write documentation. You'll see me on the forums answering people's questions about Vuo.
I've been developing apps and frameworks for several years (since I was in college). Pre-Vuo projects include Kineme Quartz Composer plugins, iOS apps for education, an app that analyzes photographs of tomato slices, and software to help people with disabilities use talking keyboards.
I enjoy using Vuo to make live music visuals. My hope for Vuo is that it will grow into a community of people of diverse backgrounds and identities making lots of different artistic, useful, unique, goofy, beautiful, crafty, wonderful compositions.
It emits a sound on start if the event from Fire on Start reaches Is within Rectangle before the initial event from Receive Mouse Moves does, in which case Is within Rectangle outputs true and Became True lets the event through to Play Audio File. You can avoid this by inserting a Hold Value node to block the event from Fire on Start.
The shader doesn't actually do anything until the scene is rendered. If you have Shade with Unlit Image going into Make Tube, the image does not get applied the moment the shader hits the tube. Rather, the shader (a set of instructions) and the tube (a set of vertices + other information) are carried along until they reach the Render Scene to Window node. On the next display refresh after that, the computer actually does the work of rendering.
At that point (render time), the GPU applies the shader to the tube. The shader created by Shade with Unlit Image is a program that inputs a position on the tube (texture coordinate) and outputs the color that the tube should be at that position — that is, the color of the corresponding point in the image. The GPU executes this program a bunch of times in parallel to color all the pixels of the rendered image.
So, to answer your questions...
Is the image going to be applied to the tube before scaling (1x1x1 tube, so image stretched to 3.14:1) to be re-stretched after the tube scaling to 1x2x1? Or is the tube "constructed" first (with scaling) and than the image applied to it?
The image isn't mapped to / painted onto the tube until the tube is rendered. No to the first part, yes to the second.
if I create a very detailed tube with > 100 lines and apply a live image to it, is it better to reshade the tube lower in the node pipeline with some Change All Shaders or can I apply it directly on the tube node and only the shader part of the node is being recreated (and not the whole tube).
With a frequently changing image, using Change All Shaders would probably be faster — not because of the shader, but because it saves Make Tube from having to do its work every time the image changes.