You're the best Toby!
Thanks for sharing,
Case #02992041 with Tableau Support. We closed it. They said they will document the low disk space behavior I encountered during the site import. Unless I pursue a solution they won't spend more time on it (at least for now, who knows for later) and that makes sense. I hope better error handling will be considered with the next iteration, that's all. As a developer the lack of good & informative error handling has always been a pet-peeve of mine.