I don't know that there is a guide per se. when idle the agent eats up maybe 1-2M of memory. so it really depends on what you are doing that determines CPU and memory utilization, etc.
if you're deploying a package you'll eat up as many resources as you would if you were manually installing the package, or if you're doing a compliance scan that scans for world-writeable files, you'd eat up whatever running those commands would if done by hand - the agent doesn't add much overhead.
because the agent is 'speak when spoken to' it does nothing unless you direct it to do something - no phoning home, no back and forth network traffic between the appserver and the agents, etc. so there's not much impact.
now, if in the past you were running around w/ CDs and installing at the console and now you are deploying over the network, you'd see an increase in traffic, but that's because the delivery mechanism changed...