Dynamic view listing nodes in proximity dependent on taxonomy term in url - which is not attached to the node itself
This is a broad question and becomes difficult to answer clearly. There are too many things to do and too many details to resolve. It looks a bit like you are trying to eat an elephant with too many missing teeth. I agree that you will need to create a custom module and by the description you gave, you will need knowledge of php for server side (pre display) and Javascript for client side action (after display). The first thing to do is get do some exploring in the structure of Drupal and how it operates.  From my own experience I know that a couple months of exploration has made a tremendous difference in my ability to solve a problem like this. Do you have any programming experience? If not start with php basics. Then move on to Drupal.

There is an excellent video tutorial series at buildamodule.com.  It charges for some of its content, but it covers a lot of ground.  Building a module will require php/mysql expertise (book:Beginning PHP and SQL by W. Jason Gilmore), an understanding of Drupal operations (book: The Definitive Guide to Drupal 7 publisher:Apress) and a solid knowledge of the key modules (book: Drupal Building Blocks by Earl &amp; Lynette Miles).

You'll know your ready when you find yourself looking forward to writing a custom module.