Wsowka, OpenManage Essentials with a SQL Express database can support up to 500 devices, as seen on page 19 of the manual found here. It also shows the other configuration requirements as well. Let me know if this answers your question.
Can anybody tell me if there is a limit to the number of devices that can be monitored in Essentials when it's configured to use SQL Express as the back end database?
OpenManage Essentials SQL DB