Yes, apart from the flashback gameplay in Kalm, Sephiroth first appears in the ship from Junon to Costa del Sol.
If you see the trailer you realize there is not much of the game shown apart from some walking, fighting and cutscenes. They didn't show any of those things you mentioned which doesn't mean that they won't be present in the remake but that we can't state for a fact that they are there either.
Indeed but it is what I fear about the game, in exchange for 'coolness' and 'more Sephiroth' we'll lose the more intricate details of the story, gameplay and battle system. I hope for great thing but 3 games instead of 1 already ruins that.