I'm not so sure that Chad and Kazuma would work, Kazuma talks too much and is really cocky and arrogant. Chad is tall and silent, hardly talks and does even like to fight back. They are two extremes I would says than similiarities. He might be closer to Kaze from FF: Unlimited, though Kaze still shows up and fights briefly the rest of the time he is a silent man. Though Kaze maybe a little to introverted to be similiar to Chad.

The Kenpachi and Byakuya fight I think Byakuya would even up winning. While I have not actually seen the episodes where either fights Ichigo, Byakuya was able to keep up with Ichigo at Bankai, who is one of the fastest characters in the show. And he had to use his Hollow, unintentionally to actually over take Byakuya, so I would say that Kenpachi would have trouble even touching him. He might be able to take him down in one strike, but if you can't land a single blow because the enemy is too fast then Kenpachi is just going to get cut up until he bleeds himself unconscious. Kenpachi would just take it all, but he would still lose eventually if he can't keep up with the speed. And I know that Byakuya's control of his Bankai increases when he uses his hands rather just his mind.

In the Hitsugaya and Mayuri fight I think it would have to be Hitsugaya, since I read that Uyruu beat Mayuri. And if Uyruu could do it, I think Hitsugaya would be able to beat him. Plus as said, Hitsugaya has long range ice attacks. Mayuri would probably flee though before the final blow would be landed.

Yourichi against Gin, I'm guessing something changes with Gin after the Soul Society arc. Since I don't know about that, but I know that Yourichi is really fast and an amazing fighter even without her Zanpukto. I would say that she would probably win. Gin's zanpukto is quick to strike, but as I understand it Yourichi is really fast and talented in Kidou. Plus being the previous 2nd Squad Captain, she would be able to go head to head with Gin without much trouble.

Orihime versus the Wind Scythe Shinigami that Uyruu defeated. That battle never happened, so how you think it would have turned out. I don't even know if Orihime gets stronger later on in the show.

EDITED: Vice-Captain huh, I don't mind. Thanks for the promotion, I'm just having fun talking about Bleach.