Expanding vocabulary to accentuate (2) by necessity compromises (1) for classes of listeners / readers who are not familiar with that vocabulary superset. Which decomposes the optimization problem to "Who is my audience and what is their comfort vocabulary set?" I would expect it's >1,000 words even for ESOL listeners. However, it's certainly < "the full set of florid English words".
And furthermore, I think English writers writing for English consumers (I count myself among these, sadly) often undervalue writing in the most effective style for the widest audience when applicable (and nowadays it almost always is: research papers, comments on a public forum, blog posts, how to's, etc etc).
Does anyone have any links to courses to help develop a working minimally spanning English vocabulary for international technical communication?
This is one problem I've had with academic literature in historically liberal arts fields. "Just learn the obscure English vocabulary (before you can understand, work, or research in a field)" is a ridiculous bar to set in front of contributions.