Shadows will only manifest properly out of what the person is suppressing. So if a character embraces their horribleness, a Shadow would not manifest made of those feelings. If a character would very easily accept their Shadow, chances are a Shadow would not manifest in the first place. Therefore, yes, that would be the perfect sort for magical gas station handshake Persona.

As for school, we imagine the townspeople wouldn't want a bunch of weird children terrorizing the town during school hours, and so a donation fund will be set up to send those who have no way of paying their way to go. Of course, those who do (whether from bringing in money of their own from similar worlds or earning it through jobs) would be exempt.