Harry knows enough mind-magic to make a person forget every life memory involving the color blue, or their left arm (or cough their animagus form cough)

We don't know that he can do so deliberately. It's equally plausible that those are examples of his inability to target his obliviations narrowly enough, or even of his general inability to satisfactorily control them.

Harry's animagus form, like his Patronus form, would be a person.

Where are you getting this? There is no stated link between Patronuses and animagi, and if you're thinking of animagi in animal form being of less interest/resistant to Dementors, it is much more probable that this is because an animagus's thought patterns become more animalistic when transformed (as we know from Quirrell and McGonagall's testimonies), and animals are naturally oblivious to Death.

Cedric Diggory and the Weasley twins have enough magic to cast the spell of cursed fire, which can destroy powerful magical devices (such as Horcruxes and the Deathly Hallows).

Do we know this? The only information I recall is that Harry isn't yet capable of casting it. We don't know at what age it becomes feasible. (that and the odds of Quirrell teaching it to them seem rather low)