We will only run as many servers on one machine as is possible without causing lag, minus a large buffer for unanticipated usage. You will be able to monitor the CPU usage, memory usage, and bandwidth usage in your control panel under server health, so you will never be in the dark as far as how much of our resources are being used. (And if you think your server is lagging because of insufficient resources, please contact us so that we can move you to a less-utilized server and/or increase your bandwidth).
We have an automatic load-balancing system that optimizes the loads across all of our servers at that location. We monitor CPU usages and receive alerts when machines have passed their thresholds. We then further load balance manually and add capacity whenever necessary.