How to create a dynamic sidebar that queries posts in more than 1 category

In short, I’m stuck 🙁 I’m sort-of new to WP and converting from joomla and am also not very familiar with editing .php code. I am literally having a mental brain block as to what to do here…

I am working on building a website for a client that needs to organize their content in the following way:

There is 1 post type = “policy”
I have created 3 parent categories and each of them have several children (sub-categories) for organizational purposes.

For example:
Region
– SE State
– NE State
– Central
School District
– City 1
– City 2
– City 3
Topic
– Affirmative Action
– Hiring
– Workplace Safety

So, a single policy (aka. post) would be assigned to 1 School District, 1 Region and 1 Topic.

I want the sidebar of my website to show the following information when a user selects a Region or School District from the top menu category.
(a) a listing of all school districts or region they selected and
(b) a listing of all the available topics posted to the region and/or school district.

Or, if they pick a topic, such as Hiring, the sidebar should list all School Districts and Regions that have policies posted to them.

Technically, the school districts own the policies so that should be the parent category. I considered having the Region as tags and keep the category of Topics.

I just really don’t know how to accomplish this? I’ve been working on this for days and can’t find the right combo. I’m beginning to doubt the organization of my site now.

Help and guidance is much appreciated.