Morpheus74, to the best of my knowledge, the only way to delete a Poser folder is to go outside Poser and to do the deed in Windows (or Mac).   Similarly, I believe that a new Poser runtime folder has to be created outside Poser, too, before being added as a new runtime within Poser.   Occasionally, Poser content is badly packaged and needs to be moved manually to correct destinations;  that has to be done outside Poser, too.   I don't think that the Poser library organisation is sufficiently sophisticated to be easily damaged by any of that.

Regarding the question of where to put hair libraries, I think Acadia's idea is best.   I generally use TY2, Miki 2 and G2 (mostly Sydney), none of them lavishly supplied with dedicated hairstyles.   Fitting a hairstyle to a new figure (i.e. not one of those intended by the vendor) is generally pretty easy, so categorizing hair by character is unnecessary.   I have recently started the looong process of re-installing all sorts of Poser stuff on to a new machine, so I have been giving these questions a bit of thought, lately.   I didn't have a separate Hair runtime before, but it certainly makes sense now.