Tooru has been a disciple of AFO from the beginning, and her invisibility powers are the ability to deprive things of sensory input with the world around them, even down to touch, until she decides to release the ability. She's got a lot of Aizen tier fights coming, but she's still just infinite prep and sneakiness, only human level strength.
Kaminari is part of a yet unrevealed class of villains. His mysterious actions in the first year are a red herring for Tooru, and his exoneration is a red herring for his proper reveal. Bakugou's the one who eventually takes him out, 'You're going to regret the day you ever came to this school' is the first thing Bakugou said to Kami on the bus
Ochako's gravity powers are enventually going to evolve into proper wormhole manipulation. Her barfs aren't just comedic, they're excess potential energy displaced with her power, overwhelming her body's senses, and when properly handled, they will be able to create portals in time and space. Ujiko is a Punished Ochako sort from the future, that comes from a time where certain events never came to pass, and the villains' growth necessitated her involvement. Ochako has been communicating with Ujiko, perhaps unaware of her full extent of her mission, but only that she's got a role to play that involves taking some darker paths.