Thank you for such interesting question. A *big* question.
Since this is a project with three phases, each phase encompasses a different methodological approach, according to the subproblems embedded in the question.
The first phase will consist on a exploratory survey. Traditional data gathering and statistical analysis (descriptive statistics, Principal Component Analysis, Multilinear regression). I aim at observing scholars' practices. Within this phase I also forsee interviews, so qualitative analysis will follow using thematic analysis.
The second phase will consist on development. There the methodology of User testing will be doubtlessly the most appropriate.
The third phase will consist on testing and impact's analysis. Users' surveys, learning assessment, and data-driven research based on learning analytics will probably the most suitable methods.
If you are interested on the second phase keep in touch and we can discuss on the best user testing approches...I still have to study that: I have a broad picture of what I want to achieve, but I have to spot the issues and refine methods along the way.