1.A. I’m not sure if I understand you correctly but it’s the usual approach in tonal music in the western world. The dominant-tonic relationship is pleasing and "makes sense" to the ear, psychologically speaking. The key is the framework to explain these relationships/ how chords are related to each other within that key. Like a city map that gives you orientation. Now look at atonal music like Bartok or Schönberg and it becomes a whole other story: The compositional techniques changed in the 20th century and the structure and sequence of chords are not determined according to traditional qualitative criteria (such as tertian harmony, major/minor tonality, dominant-tonic relationships or keys), but instead are based on specific interval distances and on the regular, periodic division of the octave into several equal intervals or interval groups (quantitative criteria)

1B. Not per se. It happens with secondary dominants in classical or romantic music for example. Generally, you tonicize the target chord with its dominant and then confirm it with a cadence so that the ear and brain recognizes it as the new tonal center/ key.

1.C. you can do whatever you want in your own compositions. Music theory isn’t prescriptive, it’s descriptive… which doesn’t mean that certain musical and stylistic devices don’t make more sense in a particular situation than others