Here some suggestions from the already existing literature on the subject:
Christoph J. Scriba, The concept of number, Bibliographisches Institut
Mannheim/Zu"rich 1968 (= B.I-Hochschulskripten vol. 825/825a).
If you and your colleagues are willing to consider non-English literature
as well, there are two more German books:
Helmuth Gericke, Geschichte des Zahlbegriffs (history of the concept of
number), Bibliographisches Institut Mannheim/Wien/Zu"rich 1970 (=
B.I.-Hochschultaschenbu"cher vol. 172/172a) and
Johannes Tropfke, Geschichte der Elementarmathematik, fourth edition by
Kurt Vogel, Karin Reich, Helmuth Gericke, Walter de Gruyter Berlin/NY 1980,
especially chapter 1.3 "Der Zahlbegriff und seine Erweiterungen" of this
very carefully researched book.
Ivo Schneider