The extra fabric just below the neck at the back is an easy fix by itself.
Your approach and analysis makes sense.
Adjustments related to shape of shoulders or any other fit issue is best addressed by looking at images of how the Luxire shirt fits. It gives us the idea of how to shape the yoke or what to change on the pattern for the next iteration.
Part 2 of your question:
I read a couple of times but was not able to bring myself to understand it. Please elaborate.
What I mean is that little 'book' of fabric samples to present possible options. Something like this:
It might be in different arrangement, smaller pieces etc.