Well, it's not too tricky really. The SW galaxy is wide and big enough that a teenage Corellian, a shaggy-haired blonde kid living at a remote moisture farm on Tatooine and the adopted daughter of Alderaan royalty shouldn't be running into nor know one another before they're supposed to in A New Hope.
Nice. Well said!
Actually I'm hoping for lots of Leia and none of Luke. Luke's closest affiliation with the Rebellion is that his friends leave to join before he reaches maturity. That's not much to draw on, unless we see his friends point of view joining and fighting the empire.
There's so much potential for Leia! Maybe as a child she started helping her pop out with running info for the rebels. I expect to see lots of excitement on board the Tantive IV.
Not sure about Han... if they plan to do standalones based on him at some particular age then maybe he doesn't really have a place in this series... who knows?
What will likely end up happening is an all new cast of characters with some familiar faces sprinkled in here and there for good measure.