May I have some suggestion in this proyect.

I will like to built a site with classifieds and directory in mind niche but I will like to have some suggestion on what theme will fit better for these purpose also what plugins should I use in order to accomplish this task keeping in mind also the SEO and friendly interface for users.
The classified and the directory section will by country by state by boroughs all with the same categories where possible.
Hope you can help me with your suggestion.