There's a lot of good questions there LM. The backstory of Cora with Zelena and then Regina has always felt slightly jumbled to me and certainly the man they say is Zelena's father never made a lick of sense when you consider how powerful she was from BIRTH when her anger/distress summoned a cyclone. Both Cora and Regina has to be TAUGHT how to use magic by Rumple. So while their family may have some innate magic in them, it has to be taught or they live ordinary lives I'd assume. So why WAS Zelena so powerful?
The Lancelot thing has yet to be explained. Hopefully we'll get to that in 5b.
Other good thing to keep track of are the 'true love' kisses. By that I mean it has to be proven by a curse break that it was true love, so we have Snow and Charming (sleeping curse), Belle and Rumple (dark curse, briefly), Emma and Henry (original world hopping curse), Philip and Aurora (sleeping curse again)... I'm sure there have been more, but I can't remember at the moment.
Also we could keep a count on how many times Belle has been shot/kidnapped/put to sleep/heart controlled/babysits/found the answerin a book/done something stupid... the writer's really need to find a new punching bag.
And how many 'portals' have we seen between worlds? Remember when Rumple took something like two centuries to find a way to get to our world? Now they do that every season at least once!
Dark curse - three hearts eaten so far (as I recall)... Henry Sr./Charming/Merlin
Magic Bean - They really need to work on growing these to some some hearts
Jefferson's Hat - destroyed?
The Sorcerer's Door thing - goodbye frozen arc peeps
Magic Tree/Wardrobe - Emma, Pinocchio in season 1 and later Cora uses the ashes and I think Emma and Snow use them to get home?