This is a broad-based question around delivering a javascript library that other web developers will use on their site. Here's the scope of my library:
Now, to my question: what's ideal in terms of best practices for providing a service in the form of a JS library such as I've described? Standard Googling has not given me much to go on, but references to guidelines are greatly appreciated.
Doesn't sound like something I'd use. The fact that you want it always hosted on your server leaves any consumer of the service open to you substituting malicious code after they've reviewed and determined its useful and safe. Thus I'd see limited uptake for it unless you're a large corporation with a trustworthy reputation.
No comment on you personally, just how I'd view something like that and how Information Security overseers in larger companies would likely view it as well.