His story seems pretty straight to me, but I might think of something and add it later. I think he was Tifa's boyfriend before they found Cloud and after his wife died.
As I said, I think she was Barret's girlfriend. I believe her and Vincent have some sort of connection, but I don't know what it is yet. I believe Lucrecia ties into both of their stories, not just Vincent's.
Nanaki seems pretty honest with his past, aside from the obvious things he hid (the Jenova injections). Hmmm... I believe he ends up marrying Shera, but that's it so far.
For some reason, I believe she likes Vincent. This is another person that I can't think of anything else... oh well. Hmmm... Something seems very strange about him, but I don't know what it is...
I believe that Vincent is NOT Sephiroth's father. There are several reasons I believe this: Hojo calls Sephiroth his son. Now, he could say that because he thinks that because he was the one who actually made Sephiroth the person he is today. Also, unless Lucrecia wasn't very true to Hojo, she wouldn't have conceived Sephiroth with Vincent. Yes, I know, NOW she loves Vincent, but before she was going out with Hojo. Well, that's about all with Vincent. He still remains a puzzle, though, so be sure and tell me what you think happened to him. Okay, first off I think Sephiroth is Vincent's stepson. He has to be, if he was conceived from Hojo and Lucrecia, and Vincent and Lucrecia are lovers. He has a VERY strong love for his "other mother", Jenova, and I believe that is strange... Second of all, if nobody can harness the power of the masamune, why can you get one in the battle arena of the Golden Saucer? Sephiroth is as mysterious as Vincent, so don't forget to mail me what you think.