Your list is exactly right..this is the chain of process I am trying to reach.
Robin2:
Why can't all that be done a lot more easily on the PC without any need for an Arduino, never mind 4 Arduinos?
Again, this is an art project. I know and I actually know how to do this as a web app. But the decision here is purely aesthetic and not very logical. Yet, the idea is the standalone Arduinos should work on their own and can be installed anywhere. It is a kind of an "internet of things" approach.