I would really like to obtain a book on Plan 9's design and ethos. Do such things exist?
Anybody have a recommendation?
(Asking here on the basis that Plan 9 was once meant to be Unix's successor, AIUI)
cat-v has a Plan 9 doc archive that contains a number of papers, manual pages for various editions and other interesting miscellanea.
Introduction to Operating Systems abstractions using Plan9 from Bell Labs might be of your interest.