Save the Sonichu possession and incest arc for the sequels so there's room to up the ante.
The first Chris Chan movie should be like Human Centipede 2 where you're never quite sure what is real and what is fantasy. The plot can revolve around Classic Chris vs The Trolls, where the audience sees him surf ED and rage out. He makes his impotent videos, though they come across as slightly less pathetic becase fiction requires suspension of disbelief, then he runs into random trolls in the real world which may or may not exist.
He prowls the night like Taxi Driver, meeting random gal pals (Ivy, Julay, etc), and commits escalating sexual harassment/assaults including getting into Kasey's pants Revenge of the Nerds style.
The movie peaks with the destruction of 4 cent garbage building via Chris' rock, filmed similarly to American Psycho's mental breakdown (where he was killing policemen and police helicopters were after him only to strangely disappear) so it's open to interpretation how much was in Chris's head.
Barry Keoghan is the right kind of disturbed to play Chris. He won't even need to gain weight because Chris doesn't know he's obese.