Django Auth user as well as custom users table?
I understand you might not still be looking but it might help someone else. The best way to do this, in my opinion, would be a simple OneToOne or ForeignKey on your new model to User. In the admin you can override the User admin and add an inline:

class FbDetailsInline(admin.TabularInline):
    model = FbDetails
    extra = 1 # Or however many you would like

class UserAdminWithFb(admin.ModelAdmin):
    ... # list display etc.
    inlines = [FbDetailsInline]

admin.site.unregister(User)
admin.site.register(User, UserAdminWithFb)


You can then set up a signal to update the relevant info and then view in the admin directly with the user.