Add Functions to a wordpress theme

I have a Wordpress property listing theme and I would like to add 1/. A function to allow me to call all properties in a certain area to display on a page for that area i.e. a 'condo in area X' page would display all condos with area X taxonomy or category. Not sure if it would be best to do that by taxonomy or category. Prefer to have the option to do this by shortcode. 2/. To be able to call a function preferably by shortcode, that displays on a listings page showing (i) property at the same condo (there is already a taxonomy for this) and also properties in the same zipcode or area also taxonomies for this although it could probably be done by category.