Limits and considerations
Here is a list of useful-to-know limits about using approval processes (as of the Spring 2020 release):
Total active approval processes per org: 1,000
Total approval processes per org: 2,000
Total approval processes per object: 300
Steps per process: 30
Actions per section (initial submission, final approval, final rejection, recall): 40
Max number of approvers per step: 25
Max number of characters in approval comments: 4,000
Approval submission is a manual operation (users have to manually click the Submit for Approval button to start the approval process) but you can automate this using Lightning Flow or Process Builder.