First off, it's "Rey" and "Finn". Second, here are just a few quick guesses I had.
1) Rey was born in the same way that Anakin was, with no father. This is the reason she is drawn to Anakin's lightsaber. Everyone is thinking she's Luke's daughter, but remember it's not just his lightsaber. Her mother left her on the planet and traveled to the new Jedi order, led by Luke, to discuss her daughter and was caught up in Kylo's rebellion and killed.
2) Finn has no force ability. He will, however, be captured by Kylo to draw Rey out of her hiding/training with Luke, in the same way Han and Leia were captured to draw Luke out of training with Yoda.
3) This guess is one I kinda agree with the "Star Wars conspiracy theorists" on. Snoke is the spirit of a former Sith Lord, Palpatine maybe? If the Jedi have the ability to become one with the force and show in spirit form, what's keeping Sith Lords from having the same connection and ability to take over bodies. At the end of the movie when Snoke says it's time to complete Kylo's training, I am leaning towards that meaning he will take over his body.
4) I think Leia is going to be the only one to survive all 3 new movies. How Luke dies or when I don't know.