Information about this service? How can we plan for new digital reference in a library?

You can find information on this service at http://www.libraries.fi/en-GB/ask_librarian/keywordquestions.aspx?WordI… It's the archive of this service and there are answers to several similar questions than yours.

Information on your second question:

Ifla Digital reference guidelines http://archive.ifla.org/VII/s36/pubs/drg03.htm

Overview on services in 2009
http://www.teachinglibrarian.org/weblog/2009/12/digital-reference-servi…

Virtual reference best practices : tailoring services to your library by M. Kathleen Kern.
Chicago : American Library Association, 2009.

The virtual reference handbook : interview and information delivery techniques for the chat and e-mail environments / Diane K. Kovacs.
London : Facet, 2007.

At Google Books http://books.google.com you can find several books on your subject by writing Digital reference services or virtual reference services. Part of them are a bit old, though.