It would be very hard for me to specifically answer your question as my usual job role is a big data developer and not administration.
1) The core configuration files all have defaults and changing the values of the file is not baseed on some science but on per-cluster base. Remember that they are other factors that affect the performance of a cluster that you have listed including node resources, network configuration and the likes. In a real world instance, there resource vary from cluster to cluster. This also should affect the config settings values.
2.I don't have any experience in stress testing as it is not my role in any team so far and even in the future. I am ultimately a developer.
sorry about that , Michael.
I will go through the this session material and will have some questions which need your help.