The CPU, memory, and disk requirements that meet the needs of a particular environment depend on the number and type of objects in your environment and the data collected. This includes the number and type of adapters installed, the use of HA (High Availability) or CA (Continuous Availability), the duration of data retention, and the quantity of specific data points of interest.
VMware updates Knowledge Base article 2093783 with the most current information about sizing and scaling. The Knowledge Base article includes overall maximums and spreadsheet calculations that provide a recommendation based on the number of objects and metrics you expect to monitor.