Re: When is external JS actually called?
Continued research supports your answer. Based on the options that look to be available I'm leaning towards simply mirroring the current site, remove some of the non mobile-friendly entities and publish a low-bandwidth version giving the visitor the choice. There does seem to be a handful of options for calling specific scripts based on viewport size or device type but these look to be inconsistent in determining which are which. Add to that the ever changing resolution for mobile devices along with the connectivity inconsistencies within device types and it seems optioning the visitor with high or low bandwidth versions is the way to go.
I also learned that simply placing display:none in a media query does not prevent site properties listed in the HTML mark-up from being downloaded (there are some options but they are just as spotty as mentioned above). This is another very good reason for two site versions.
Again, appreciate your reply!