Using custom taxonomy "under the hood" only – Insight plz?

Ok. I am developing my own theme for a website more or less from scratch in terms of css/html design and also PHP.

I need to organize and present posts in different ways beyond just a “blog” that lists things in order by date.

So I’ve practiced and familiarized myself wp_get_meta and using meta data, which is useful at times.

But I find that using a custom labels/tags taxonomy seems really good over meta data for doing other stuff like using the WP_Query object to query posts for building lists and other loops:

Example #1: I want to construct a list of posts that meet a certain condition (only need to display title and date during the loop). I want to have this list exist dynamically inside of an individual post. So I could just use a custom taxonomies label like “label-123” and create a WP_Query object that pulls all posts with that label. I’d just have to toss the required conditions into $args. Build that process into a short code function with a custom loop and done.

Example #2: If a post as a certain labels/tags of my custom taxonomy certain functions would execute in my sidebar to display different information. In other words I’m using them for quick “if { … }” triggers in my UI design of my theme.

I don’t want this taxonomy to exist in any purpose to the web visitor or crawler bot. Internal, under hood php coding use only. Absolutely non-existent.

So I pose 2 questions:

1 – Is it feasible to use a custom taxonomy in such a fashion – disable any working URLs associated with this taxonomy so it completely does not exist to the visitor or search engine bot etc. How would I do this? Does this make sense to a seasoned WP developer?

2 – Is this considered bad practice? If so is there a better way?