Erik Kostson
Ansys Employee
These question would be covered in a full course, and something we can not really do and cover in detail here in a forum.
I would recommend getting a course in linear and nonlinear dynamics as the one given in our learning hub (paid service).
This course covers the missing mass and rigid response and other topics, which I think are necessary (to have an understanding of these things) if we do this type of analysis for real structure and projects. Thus I would strongly recommend this course if you do analysis as part of your work (not student work, so commercial work) on real structures.

All the best