I can't answer all your questions, and I'm hardly well versed in younger trainees, but I think that if the lifts are being done properly there should be no asymmetric muscle development. Imbalances should be fixed with proper form, not ancillary stuff (though the latter of course is great for assistance work when the time comes).
Hopefully someone else has some answers to your other questions.
If I may inquire, why did you not start with cleans in the program? Why nothing to replace them (e.g rows)?