o The syntax page says that gif, jpeg, and png files get embedded as images. Where in the code/configuration is this specified?
Hardcoded in parser/renderer
o Is it possible to disable image resizing?
o Old images/files don't seem to end up in the attic. (Maybe I'm looking in the wrong place...) Is there a way to enable this?
dokuwiki has no revision management for media files
o Can uploaded files be deleted directly from the filesystem, or is there an index that would also need to be updated?
yes, you can just delete them. (Of course pages referencing them will point to broken images then)