There is no single source list for editors and it is not possible to tell from a list how good (or bad) a particular editor may be. If you are looking for an editor, PM me and tell me whether it is for fiction or nonfiction and what you expect the editor to do; I'll send you some names.
The best time to hire the editor is after you have completed your manuscript, at least the first draft. That is, assuming you are looking for a developmental (substantive) editor. If you are looking for a copyeditor, then the time is after you have what you think is a final version ready to go to print (figuratively).
For a discussion of what different editors do, see
Editor, Editor, Everywhere an Editor. For a discussion regarding finding a professional editor, see
Finding a Professional Editor: The Needle in the Haystack Problem.
For insight into the editorial process from the author's perspective, see Vicki Tyley's guest article,
The Editor: A Writer’s Fairy Godmother or Ogre? And, finally, to understand the relationship between an author and professional editor, see
Symbiosis: The Authorial and Editorial Process.