1. You can configure the Geo Settings from within the
Vantage admin dashboard to suit your location.
2. If you wish to add a custom field for this, you could. Ideally though, you'd make use of the business contact form built into the theme so as to avoid your users email addresses being harvested off your site by spammers.
3. You can make modifications to the emails through customization of the default theme, as these are not specific options available in the Vantage admin dashboard.
4. There is no specific maximum image size settings in the theme itself, however WordPress itself has a limit of 10MB and this could also be affected by what your hosting provider allows. You could customize the theme if you were wanting to restrict upload sizes.
5. Yes, you can set moderation on listings before they are published. Thanks.