1. Yes you can most certainly create your own child theme if you wish, and we recommend this is you are planning to make modifications to the default theme in any way. You can find useful documentation relating to this on our
AppThemes Developer Center page.
2.
a) Of note, there is an
existing ready made ClassiPress child theme called Grid which offers the display/layout mentioned.
b) There is no setting for this within the theme, so it would require customization on your part.
c) Again, this would require customization to add it to the homepage, however you may wish to note that there is an advanced search functionality built into the theme already which includes location based fields. This can be seen in the category view sidebar as shown on the
ClassiPress demo site here.
d) If you're only using one parent category/genre, it would make sense that you'd set up those subcategories as parent categories would it not? The theme settings allow you to display parent categories only. Thanks.