You can do most of this - go to the “edit” page for the category, and choose the “settings” tab. There’s a setting called “custom incoming email address”. Set this to what you want for the category.
If you turn on the “enable staged users” site setting, then “staged” users will be created when people send email to that address.
However…
As far as I know, this won’t happen unless the user actually signs up for an account.