I completed your questions, but then wasn't too sure if my answers, or lack of answers would help you. Decided to post anyway.
Sketches become Cadd plan. The Cadd plan is used to create a 3d model (with sub blocks of all interior and exterior elevations). The Cadd model is further organized as blocks (SU components) to organize textures. The model is ported to SU for visualization, and presentation. Typically some kind of animation, and quick renders.
All design revision are done in Cadd then ported to SU (as revisions to components) so that the Cadd database is preserved for production drawings. I find this process faster then designing in SU in order to port to Cadd.
I do not depend heavily on plugins, and try to use SU as it was created to aid in visualization, and presentation.
Various render, and post processing software.
Nothing, except for a small library of components, and materials that I like to use.
Inexpensive software, intuitive interface, and easy to use. Photo match, shadow, and style features.
Don't know if its a weakness, but it would be nice if some of the editing tools were more like my Cadd system (especially the stretch window, better window controls inside a command, and selective unselect). Also nice if SU could dde with a spreadsheet, but not if it slows the app down.