He got all of Rukia's powers because the Hyougoku inside of her reacted to her wish to suffer/redeem herself by saving Ichigo, so it gave him all of her powers. This was said flat out by Aizen himself.
Isshin's powers have been back for a while, he just didn't reveal it/had a need to use them.
Ichigo got hollow powers because he partially hollowfied in the Shattered Shaft during Urahara's training.
He got bankai quickly because he cheated by using Urahara's dolls.
His hollow powers didn't evolve in Hueco Mundo, they got stronger because he learned to control them and increased his mask retention. On the dome against Ulquiorra, he completely lost control over them and became a monster.
He has Quincy powers because his mother is a Quincy. He is a Quincy/Shinigami.
I really don't know where your theory is coming from. Its even expressly stated early on that only Quincy absorb reiatsu from their environment to use their skills, as we see with Ishida after taking off his glove against Mayuri. Shinigami run purely on their own, self-generated power.
As for the chapter:
So glad we didn't waste time with Grimmjow. Really, I have zero idea why Kubo even brought him back, aside from the fact that he mishandled the Hueco Mundo Arc so badly that he didn't even wrap up his ultimate fate and had to bring him back to satisfy fans and tie up a loose end. He has no place in the storyline, his job in the narrative is done. But at least he didn't derail the chapter with him.
Welp, Ichigo is related to the Shibas. Nobody was surprised. Kubo has been telegraphing this plot twist since SS Arc. All it does is fill in a lot of gaps in the story concerning the Shibas and their fall from grace. The big question here is why "Uncle" would be sad to see Ichigo go to the Royal Realm. THAT is the big mystery here. Something there - possibly this technique that will reforge Zangetsu - will do something that takes Ichigo off the path that Isshin wanted for him. Mmmm...
Again, Ichigo is a really great actor when he wants to hide something. Im reminded of the parallel in HM when Grimmjow of all people tells Ichigo that just because Orihime is fine physically, doesn't mean she's fine on the inside. Same thing is happening here. He's torn up about Juhabach's revelation. He probably wants to go find his father and get some answers. But even then, he does what he needs to do to be able to protect. I dont even know why Chad of all people even ventured down that path of conversation.
But still, props to Kubo for actually getting us to the Royal Realm relatively quickly. I see a lot of houses there. The Royal Realm seems to be pretty populated.