I really like what you have here, it's a very nice outline.

I want will add a few things here:

Michael Corleone: Has always been a victim of his own ambition and knowledge of running crime family. He is always sucked back into doing the easy thing instead of doing the harder, right thing. I think he should reluctantly give advice to Vincent and advise him in what to do. His advice will be crucial for the less wise Vincent to continue down a negative path set out by him and his father. Namely he will have a hand in Pregento and Hauser. Through his advice, he will not make any value judgements, but still at the same time have a hand in what is to happen and along with vincent hold piece of the puzzle for figuring out the role of Pregento and his true identity. In his advice being a recant of history he will be encouraging vincent and although not activly not doing anything will still be insturmental in what happens and is guilty of the same crime that he was in the whole GF series.

Vincent: Is alot more sophisiticated and complex in this one. In GF III Vincent wasn't fully concious of the reprecussions of what the life can entail in this he is sadder and wiser for his loss. Vincent is offered a majority ownership in the team to help convince Gentry to sign onto the team. Knowing a good opportunity when it presents itself he doesn't just float Hauser a loan, but demands ownership of the team from Hauser for this favour, pointing out that Hauser will still profit. Hauser delays on the ownership handover due to the league ownership approval process.

Gil Hauser: Although he still retains majority control of the team, the team is about to become bankrupt and therefore to save the team he must turn to Vincent to delay this and getting him to get Gentry into the mix. Gentry is the only thing that can save the team. when he was drafted and instantly improved the team he was drafted for say the Cub's fortunes and their attendance. The backstory for Hauser is he owes Controvino for the original loan to get the ownership in the team. With the team going bankrupt and his finances scarce, he is dead if he defaults on this loan. That's why the Controvino plans to move the team.

Controvino: Knows Hauser from his work with the LA Angels (Hauser worked for them) and had some dealign in terms of fixing games. Floated a huge loan to Hauser in the early 70s to buy majority ownership in the then prosperous team. He as such has been collecting part interest in the wake of the teams diminsihed fortunes and the remaining interest has caused Hauser's debt to sky-rocket. He threatened Hauser's life and Hauser has no choice but to go along with Controvino's plot of moving the team, which will allow Controvino's construction rackets to bilk the city for millions and his legit construction company will get the contract for the stadium as per his bribes in the way of party contributions to his party. For this service Hauser will retain ownership of the team and have his nefarious debt erased. Hauser turns to Vincent because he fears no more favours will flow from Controvino, and not wanting the financial situation of the team to truly be known by C, he must turn to Vincent for a favour. But Vincent demanded more than he is expecting. He then goes to Controvino with this problem and Controvino tells him to play along, knowing he could get more money out of this and stay hidden if he kills Vincent.

Gentry: Surgery in the off season has bandaged his knee and delayed the inevitability of of a serious problme occuring with his knee. His doctors were paid to give him a clean bill of health. Hauser saw a solution in Gentry, that's why he bribed the Dr's. Hauser, knowing he could over the course of a season bail the team out of their short term debt and keep the team in NYC and under his control until he could arrange the move with the league, he paid the doctors off to give Gentry a great bill of health.

Anthony Corleone: After the death of his sister Anthony has hit the bottle then the gambling tables. When his mother had a stroke he started using drugs and after the death of his mother he switched from cocaine to heroin. His voice has suffered in the years since and by the time of the opening family scene he is almsot all washed up.

Pregento: A legitimate business man who is the most hidden Don of the whole series. He has done this by posing as a humanitarian. His mother was a Ciccio, and has an alterior motive for wanting Vincent dead aside from the profit his associate Controvino will make and float to him for helping set up the hit. Pregento taking pity on Anthony and attempts to bail him out and help save his career. He poses as a humanitarian and is called "The Saint of Little Italy", is the ultimate wolf in sheep's clothing. Vincent finds out about Pregento after Michael gives him the Ciccio and Andolini story.

Donkey Boy Assassian: After the first hit failed, Controvino lines up Donkey Boy from GF III to make a hit on Vincent in NYC and he gets far but fails so VIncent, usually fearless flees to Sicily for solitude.

Vincent's Body Guard: A kick ass hard faced sicilian (I'm thinking the main protagonist from Snatch would be great in this role), he carries two desert eagles and is cold and stoic.

Remaining Owners: Bought out by Controvino, this is Vincent's first indication that something is up with the plot, is the insistance of the Remaining owners to move to LV.