I can’t get my head around the best way to zoom into, or out of a scene. This would be an extreme sort of zooming, maybe 10,000 to 1.
Lets say you have a model of a car and you want to zoom into the finest detail. The car would be huge in the blend file to accommodate the finest detail, but as you zoom in you don’t need such high resolution for a whole car - just the part you are zoomed to.
So how do you guys achieve an extreme zoom of 10,000 to 1?
You already gave the answer to your own question. If you don’t need the whole car… Well, don’t render the whole car. 
Meaning: Cut your car into pieces and set what you can’t see to not render. Just animate the “renderability” of the different parts in the Outliner. And if you have problems with lights, shadows and reflections because of missing parts, replace theses parts with simple planes or, at least, lower resolution versions.
Think like a game designer. Out of sight: No render. Far away: Low resolution.