Can use taxonomies to I build a list of "conditions" that can be added to and referenced from different nodes?
I'm not sure if you can get this done with taxonomies. However I would recommend you to have a look at either of those modules also (or &quot;instead&quot;?):

Entity reference.
Entity connect.

These 2 modules are also recommended in the (illuminating) article &quot;Relativity Model for Drupal&quot;, for which this is an introduction to it (quoted from this linked page):

The Relativity Data Model for Drupal is a zero-custom-code, collection of steps, procedures and methods that strive to help site builders, users and site visitors interact with Drupal in a far easier and more efficient way. This is done by:

Data architecture and data modeling merging as a single step through a documentation procedure.
Customized user interfaces that cater to individual workflows throughout permission roles.
Multi-level relational data structures that relate to other multi-level relational structures.
Mimicking the concept of database joins within Drupal's UI's.
Vastly reducing the size of Drupal sites by a small handful of modules that provide greater power, speed and expansion capabilities.


The small handful of modules (cfr. the last bullet) is detailed on Interface elegance and experience.