I was searching on the internet to find out the recommended hardware requirements for workflow manager server but found nothing. I have a business application with custom Visual studio workflows which will be used by about 10,000 user’s .I have configured the separate workflow server and attach it to SharePoint form for test business workflows.
After doing some performance testing of workflows I will recommend the following minimum hardware requirements for workflow manager for up to 10,000 users.
RAM: 6 GB
Processor: 64-bit, 2 cores
System Drive: 50 GB
Note: The hardware requirement for workflow manager also depends on how heavily your SharePoint application is using workflows. Also, I was using SharePoint Farm database server to store workflow manager databases.