rgleason wrote
I am inclined to put all the screenshots for each Namespace /Book into one directory folder for simplicity
That makes for simpler and more consistent media management. i.e. if media is primarily associated with a given pages namespace, it should reside in the same media namespace. When an editor works on a page the Media Manager will refer to the same namespace in media by default. However when the media is used in many (page) namespaces it's sometimes simpler to locate that media in a common namespace e.g.
$DokuWiki/data/media/common, or,
$DokuWiki/lib/tpl/$YourTemplate/images for media used as part of your template customisations.
rgleason wrote
When in OpenCPN Dokuwiki would putting this many files into one directory (728) become too slow or difficult to use?
No. You'd really only expect high system loads when those files have to be processed somehow e.g. indexing - which affects pages more than media. There may be exceptions to that imposed by your choice of file system, but it's likely you are using a Linux ext filesystem which won't have issues with such a small number of files. Note that NTFS is not a good choice of a file system for large amounts of files used by a webserver (there are also full path length limitations).
rgleason wrote
Also, if we have a number of Manager/Editors would it cause some user difficulties finding the files or not?
No - with the exception of "common" media. See my previous comment about the default namespace used by Media Manager.
rgleason wrote
-Currently the files are stored in user directories accessible by all.
I take it you mean "read and write" accessible. It's (generally) appropriate to give users the same rights to the same namespace in media - DokuWiki does that by default. Putting the media in another namespace makes for permission difficulties.
If media is going to be used in various namespaces, some of which not all users will have write permissions for - then store that media in a root media directory with read-only permissions for users with the lowest level permissions (or DokuWiki users with read-only access won't see media used all pages e.g. a help icon used for links to contextual help on many pages).