Calibre converts from “a huge number of files to a huge number of files.” My experience is that it is not a precise conversion, but is good for previewing and looking for problems.
This software converts several file formats, including Word DOC and MOBI, to EPUB files. Includes an EPUB check to look for formatting problems.
A free online service to check your EPUB file for formatting errors. My preference is Sigil for the check because the error messages are clearer.
PDF to Word
A free online service to convert a PDF to Word document for editing and formating.
A free image manipulation program.
Free Stock Photos
(be sure to read restrictions and license information)
The following organizations have listings of professional, freelance editors.