Thanks for your feedback, in answer to your questions:
1 - Yes you can determine which fields you want to appear in the refine results that are specific to categories, and no customization of the theme is required as it is part of the ClassiPress admin dashboard settings. You can read more about the setup
here.
2 - All categories and subcategories are set up by you, and you can use the custom form functionality already built into the theme to determine the fields that are specific for that form based on category. You can also find documentation about this
here.
3 - This would require customization of the default theme on your part, but yes it can be done.
4 - There is no specific newsletter function built into the theme, but there is a subscription option which does generate emails when purchased and on expiry.
5 - This is not a default feature of the theme, but again could be achieved through customization. ClassiPress is not encrypted, so essentially you can make whatever changes you would like to. If doing so, we recommend the use of a
child theme which will prevent you from losing all of your modifications in the process of an update. Thanks.