A summon is a saga creature, so it works exactly like a saga: Once you reach the final chapter, and its triggered ability resolves, you have to sacrifice the saga
Of the two, I prefer Crashing Drawbridge, but if you're in the need to pump up the damage just a bit, the equipment can be meaningful, though that extra mana matters, too
A Realm Reborn affects all permanents and can be used in decks beyond a token theme
For more spoiler stories, check out the team of strange detectives coming to Magic, or take a look at the top legendary creatures from the MTG set.
Pokemon Japan has already started posting cards from Mask of Change following the reveal of the set this morning
It's slightly narrower in archetype, but the typical strategies that take advantage of these team prowess effects cast a bunch of instants and sorceries in a row for value