Sugest use of mysqmail and libapache-mod-log-sql to bandwith control.
Im sugest use of mysqmail and libapache-mod-log-sql:
http://www.gplhost.com/software-mysqmail.html and http://www.gplhost.com/software-libapache.html
Debian package libapache-mod-log-sql Can provide realtime band statistics
Im translating DTC to brazilian portuguese and ispconfig3 too, mysqmail packages it´s so close to be stable.
If is possible cooperation for usage of this great tool provide by gplhost guys.