The Classic workflow and Process Automation are almost in no way similar. The only advice I can give on this is to break down each one of these tasks into a specific function, determine what is required for that function and then build it into Process Automation.
For instance if a step requires a managers approval, build your process with a User interaction task or an email based approval and assign it to the managers in question.
Here is an example Email based Approval process for Service Desk:
https://communities.ca.com/docs/DOC-231172137
Service Desk only has 2 ways to trigger a processes, either through an attachment to a Category or Area, in which case the process is launched when the particular category or area is selected for a ticket; or through an Event Macro where a process is launched when the macro conditions are met.