Using the same title I have an article called Main Article and I am rolling out the chapters each week (8x). So, each chapter will have the MAIN Article Title AND Chapter Title.
eg: Stories from the top of the World; The Journey of the arborists

Stories from the top of the World; The way to the top
etc, etc...

I could create the MAIN Article as a single entry (with an excerpt) but this is not the brief from the client and use a relationship field to add the chapters to the Main Article Title.

I could add the Main Article title as a category and select this at each chapter entry, but how do I create the URL format to do this? This might also be tough to explain as a workflow for the client....

articles/{category}/{slug}


What else are the options?
You can set the URL format to be anything you want really, just setup your templates and then setup some routes; then it's all going to work automatic for your client and they never have to worry about it.