In answer to your questions:
1) You can disable comments from the WordPress admin dashboard, and create custom ad forms which do not have the price or tag fields. Removing the actual price tag image will require some minor code modification on your part, but yes it can be done.
2) You can select the "standard view" option for the theme which means the "Ad categories" box will not display on the front page, and custom menus to hide other pages.
3) By default, the advanced search functionality is only visible from the category page view, so this would require customization.
4) Again, this would require customization as there is no setting for it in the ClassiPress admin dashboard.
5) Certainly, yes. ClassiPress is not encrypted, so you are free to make modifications as you wish, and provided you have the coding knowledge to make the required changes which are not able to be configured from the admin dashboard, you can make it look as pretty as you like ;)
Thanks.