In answer to your questions:
1. The built in .csv importing tool is specifically for ads, so if you're importing ads which have a category attached to them then yes it would add the category, but not categories/subcategories alone. You may be able to find a WordPress plugin for importing bulk categories, however you'd need to bear in mind that they'd need to support custom post types.
2. The existing advanced search box currently appears only in a category view, so it would require customization of the default theme on your part if you were looking to add this on the homepage.
3. If you're referring to fields not currently shown by default, then yes it would technically be possible through customization, however there are no settings within the ClassiPress admin dashboard to add them.
ClassiPress is not encrypted, so essentially you are free to modify it to suit your needs if you wish. Thanks.
