Request for advise: Appian single server scaling to more engines

Hello:

I am seeking advise for vertical scaling of a single server, in regards to adding more engines in the appian-topology.xml configuration. We are currently running the default topology with three analytics and three execution engines. Our server have 16-CPU cores and 64GB of RAM, and I am looking for suggestions on how may engines would be ideal for this given system CPU and RAM. We are looking to support 100 active users at any given time. Is there a formula for scaling to number of engines relative to system specs; or of you can share any use case examples or example of topology with similar system specs would be greatly appreciated. TIA.