For selecting a available resource from a list of resource you can use a selection expression like 'Candidate.Resource.Capacity.Remaining' and and set the Selection goal to 'Largest Value'. What this will do is, it will give priority to a Resource with highest available capacity ( in this case 1) indicating that a resource is available for seize and seize the available resource.
You can use a state variable to track the number of entities that enter the server. Whenever an entity enters the 'Input Buffer' of the server, assign the number of entities present in the buffer and the processing station to a state variable ( Using Server.InputBuffer.Contents+Server.Processing.Contents) and when the entity is leaving the server, decrement the value of the variable by 1. Use a state statistic element to keep time persistent statistic on the state variable. Use Statestatistic in the experiment response to report maximum and average number of entities.
If you share this same state and statestatistic across multiple servers, then you will see statistics about ALL the servers.