Gryffindor Rey: My big definition for sorting Gryfinndors is: "do they just do the thing? Rey, unquestionably, does the thing. She's brave and full of conviction and she decides to help return BB-8 to the Resistance without even giving it a second thought -- not because she's loyal to them, she doesn't even know them. Because she thinks it's the right thing to do.
Slytherin Finn: For reasons mentioned above; Finn as the sweetest, most earnest Slytherin ever who's greatest desire is to escape the order and be happy -- a monumental ambition for someone with his upbringing, and he finds a very strategic way to achieve that goal. He isn't loyal to a cause so much as he wants to keep himself and the small group of people he cares about (Rey, Poe) safe at all costs, and has no problem being underhanded (lying to the Resistance re: Starkiller base) in order to do so.
Hufflepuff Poe: Every single thing that we see Poe do is, in the end, motivated by his loyalty to the Resistance and the grander cause that he believes in. He doesn't "do the thing" because of gut instinct ala Rey: he's loyal to his cause and he's loyal to Finn, who he trusts almost immediately even though he could've very easily been suspicious in that circumstance instead.
Slytherin Kylo: Not because 'it's where we sort bad guys', but because Kylo's whole arc is about being ambitious, striving something bigger than himself regardless of the consequences. ("I will finish what you started.") He wants power, he fears not being as strong as Darth Vader. Even his imploring speech to Rey is based on power and achievement: "you need a teacher, I can make you stronger" because that's what would motivate him.
Re: If you were planning a TFA/Harry Potter crossover...
Gryffindor Rey: My big definition for sorting Gryfinndors is: "do they just do the thing? Rey, unquestionably, does the thing. She's brave and full of conviction and she decides to help return BB-8 to the Resistance without even giving it a second thought -- not because she's loyal to them, she doesn't even know them. Because she thinks it's the right thing to do.
Slytherin Finn: For reasons mentioned above; Finn as the sweetest, most earnest Slytherin ever who's greatest desire is to escape the order and be happy -- a monumental ambition for someone with his upbringing, and he finds a very strategic way to achieve that goal. He isn't loyal to a cause so much as he wants to keep himself and the small group of people he cares about (Rey, Poe) safe at all costs, and has no problem being underhanded (lying to the Resistance re: Starkiller base) in order to do so.
Hufflepuff Poe: Every single thing that we see Poe do is, in the end, motivated by his loyalty to the Resistance and the grander cause that he believes in. He doesn't "do the thing" because of gut instinct ala Rey: he's loyal to his cause and he's loyal to Finn, who he trusts almost immediately even though he could've very easily been suspicious in that circumstance instead.
Slytherin Kylo: Not because 'it's where we sort bad guys', but because Kylo's whole arc is about being ambitious, striving something bigger than himself regardless of the consequences. ("I will finish what you started.") He wants power, he fears not being as strong as Darth Vader. Even his imploring speech to Rey is based on power and achievement: "you need a teacher, I can make you stronger" because that's what would motivate him.