How to get statistics for selenium grid utilization
You may create a Servlet on the hub so that you can check those statistics directly from a browser just by loading the URL. Check the class RegistryBasedServlet.
Then on the node's launch script you will launch that node directly from a launcher java class that contains a loop that collects all the information you neeed on that node.
You could also use that loop to update that node configuration and re-register on the hub.
Then from the servlet, you may process all node and collect all the information. From the hub's registry and/or the servlet.