on your second point, green per/passing in a center, for yellow rebounding, is tough. i wouldn't necessarily go all rebounding there, probably would be more balanced. for a scoring big that per is pretty valuable, but assuming non scoring, i'm probably at least putting a little in passing in that situation.
the important thing is to push cores with good growth - green or blue rebounding, for sure i'd be ok 0ing passing if that is what it took. maybe even black. but for a yellow reb, that is tougher. 10 extra minutes in reb might get you 1 reb, versus a handful of passing or more, it starts to become less obvious what the right call is there. what i would say is, don't hesitate to sacrifice just about anything to put at least 20 and perhaps even closer to 30, in a high potential area like reb or ath (conditioning), especially early in the player's career. if you are 0ing your reds and non critical yellows, and loading up your high value blues, greens, and even blacks, you'll be fine. its not super important how you prioritize the low priority stuff.