In answer to your questions:
1) Yes, you can disable comments within the WordPress admin settings if you wish to remove this.
2) Through some minor code modification, yes it would be removed.
3) If you create a custom ad form which does not include location details, then the Google map will not appear in listings.
4) Yes, the issue only occurs because it is a demo. Although it is fully functional, it does not save data which is why the error appears.
5) Yes you can allow ad renewals and the customer is emailed when the ad expires.
6) You can configure the new user email within the
ClassiPress admin dashboard, but outside of that it would require customization. Thanks.