Are there any good solutions for monitoring my business cable gateway, it's the SMC gateway. I need to be able to monior bandwidth usage ideally on a per IP basis. I'd also like interface status such as link speed, packet count, error counts, etc.
PRTG is the best solution to your questions. Installed locally it will monitor for conditions and notify you via e-mail as well as granular live and archival information.
That doesn't run on the gateway router though. And I don't think the Comcast leased routers have SNMP enabled at all.