Plagueis' race in canon is undefined. the Darth Plagueis novel was thrown out with the rest of the Legends continuity. But for Snoke to be Plagueis, he would have to have survived Palpatine's account of killing him. Possible for a being that created life out of only the force?
Saying Rey is an offspring of any of the three characters is problematic. Leia/Han would have recognized her if they had a daughter (though Han may have forgotten, Leia wouldn't have). If you think it's Luke, then the immediate question is "who was Mom?" because immaculate force conception would work only on, well, a woman.
It could entirely be that all three of our main leads are not related to the original protagonists. Boyega's said in interviews that the role of Finn wasn't strictly for a black character, so Finn doesn't have to be related to Lando or anyone we know. They may run with that idea for 8 though, if it hasn't been written yet?
But the above kind of flies in the face of destiny trying really hard to get Rey to accept Anakin's lightsaber. For that kind of setup one would figure that she's part of the Skywalker legacy... or is she? One theme of this trilogy could be that greatness is not passed on by blood. Kylo is hellbent on assuming the mantle of his grandfather, but our protagonists are standing in his way.
Regarding pacing I think there were a few places that the movie felt too long. The mental struggle between Rey and Kylo in the toruture chamber I think went on for at least half a minute too long. There was another moment I forget that was similar... the want to check the watch to see if the scene was going on too long. They could have used that padding in other places.
And the sequence on Han Solo's new freighter could have been trimmed down. They could have placed the Falcon undergoing repairs on Jakku when Finn and Rey steal the ship, or had Han and Chewie pop up during the struggle from their own attempt to steal the ship back. Perhaps it worked better to absolutely have Han and Chewie board the falcon after Finn and Rey used it for a while, but the freighter sequence gave us nothing useful beyond that scene. It shows us Han being in trouble with his debtors, but the monster chase scene wasn't necessary for his character except perhaps to have Rey save Finn.
I expect once the trillogy is complete Episode 7 is going to be a satisfactory act one of a three-act long story. The excitement will happen in the further two installments, but the first act sets up the post-Endor world and introduces the new people to us. I just hope that Harrison Ford's exit of the show gives Han the gravitas that was maybe missed had Han died in RoTJ. But I think Leia confronting Kylo, not just for turning to the dark side but also murdering his father, is going to be worth Han leaving us and a major point for Kylo's story.