It is impossible to answer any of those questions with certainty until the schedule is released. For example, I can make the trip in one day from PIT to & from OGG or KOA (with one stop in LAS) about 3-5 months per year from PIT when the schedules of our LAS flight align. Other times require an overnight (typically coming home) when those LAS flights don't align. PHX/LAS will be your most likely connection points from the East Coast (possibly OAK/SMF/SAN/LAX too with a double connection). Breaking up the fares typically doesn't save me any money, but obviously YMMV in that one.
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