In Gmail there is an IMAP Connection limit of 15 simultaneous connections. Web browser users should be ok, but tablet and phone users may receive the error message, 'Too many simultaneous connections' and then have imap be subsequently blocked.
Do you also want to allow the same level of access to the account to all users? Someone could get wily and change the password.....
Have you considered a distribution list/group using gmail? This would require separate accounts for your call center users.
As far as google drive goes, there are limits on connections but that applies to sharing items in one google drive account, and collaborating with others.