Agreed. It's worth the learning curve for the sheer power you can enable your workflows. I've always wanted to toy around with node based architectures and this seemed quite easy after using A1111 extensively. The community providing ready to go workflows has made it quite enjoyable too.
It doesn't abstract away too much from JavaScript and provides good methodologies as outlined in the Learn/Guide section of the site.
As per your points:
1. A good couple of hours to about 6 depending on expertise just to test the workflow, get comfortable with MSX and to read the docs.
2. I've not used it in production as for current as I am still in an experimentation speed, but the whole premise is that it acts as a UI layer amongst the business logic that you may already have. It is fairly transportable.
3. This would be on a medium scale level depending how you couple your code and how modular you keep it.
4. Because it is fairly straight forward to get up and running. The blog posts alone provide great insight into application structure. Also the benchmark claims are quite appealing.