@EN6924
Tuning and controlling memory usage total depends on how Workflow is created in designer. It is separate matter from Server thing. I mean, to optimize performance, you have to create WF so as to reduce data size in each stream line, and exclude the waste process(typically sort operation before join, etc.).
Server itself doesn't know how long it will take to complete WF before start running and even during running WF. They just put job one after another once the previous job is finished.
If you are talking about Server sizing, you can refer to official documentation for system requirements, and how to assess the number of CPU cores, RAM size, etc. Please note that the required machine spec total depend on your environment, and there is no general recommendation.
Sorry for cannot advise specifically.
