There are many ways to display problems and current status of elements in your virtual environment with Reporter 4.
Many report templates are available and you can make your own choice which ones are more convenient for you.
Here is an option for your request:
VMs poweved off: [Configuration Report] from [Offline Report Pack - Infrastructure] is good to see which VMs/vApps are running/switched off/inaccessible. Powered off VMs are drawn without little green markers.
Low disk space: [Datastore Utilization Report] from [Offline Report Pack - Infrastructure] is handy to determine which datastores are over utilized, under utilized and normally utilized.
CPU/memory/etc usage on servers: [Host Performance Report] from [Performance Report Pack] will show you a graph with CPU/memory/etc utilization. With this report you can determine, for example, top consumers of resources.