@MarianT Thank you so very much for the detailed answers! I have a much clearer idea of how to go forward now.
Besides my curiosity regarding reggikko's questions (unique friends or not; treatment of San Myshuno and Magnolia Promenade), I have a few more questions.
Edited to add on August 30th: I've withdrawn all my questions. Meg's asked the most important question: when can an heir begin work on each of their requirements?
Unique skills
The rule: "2. Reach the 10th level of a unique skill."
Q6: This refers only to adult skills, right? I'm assuming "Yes."
Collections
Q7: Should each generation's collection be unique? Again, I'm assuming "Yes."
Additional lots
Q8: In addition to restaurants, a spa, and a bowling alley, may we also add a toddler park (by MaxisCreator_01) and a cafe (Maxis)? I'm withdrawing this question, too.
I have never tried out the odd jobs/freelance gigs, so I think I'll go practice those rather than worry about any new questions, lol.