A few thoughts and comments from England where Intl is the only significant style taught for social or for comps.
Prep step: Agreed it helps with initial swing. In the UK it also marks the couple as competition trained, useful to catch the judges eye but looks out of place on the social floor. Unlikely to be taught to beginners, but when the inevitable question "how does the lady know which foot to start with?" arises, social dancers would be told the leader should make a definite weight change, maybe with a small step to side or back, just before starting to dance.
Natural or reverse start: Mixed opinions and teachers preferences vary. Personally I prefer a reverse figure so that the leader has a good view of the floor before starting, rather than stand in the way with his back to oncoming traffic.
Routines: These are used for teacher's convenience. It is much easier to spot couples having problems when the class moves as a group. Alignment, directions and amount of turn are important in Intl style and affect precedes and follows. Simple beginners routines take this into account. Typically a routine would develop thus: natural and reverse turns with closed changes, using natural turns around corners; whisk and chasse, adds concepts of PP and transition into and out of PP, syncopation, and stepping OP into following figure; spin turn at a corner, easier to learn as less turn required but often means couple never manage a full spin turn and always underturn it along the side of the room; hesitation change, adds use of same foot twice. Many social dancers never do more than those figures.
I sometimes liken routines to learning a foreign language. Initially the whole class learns "the cat sat on the mat", then "the dog sat on the red mat", and pretty soon they are making up "the black cat sat perched on the white dog."
Floorcraft: Not taught to beginners, except for under or over turning, curving chasses or using hesitation if blocked. Beginner are told that more advanced dancers will handle collision avoidance. This is easier if the beginners stick to their basic figures with correct alignment so that other dancers can anticipate their actions.
