You can activate a process before you have finalized the application form if your process contains an LOI. Applicants can begin working on the LOI and submit them before you have finalized the application. The system will not allow you to approve LOIs until you have an application added to the process. If you have an application added to the process the system will automatically assign it when you approve and LOI so you will want to make sure you have your application form finalized before you approve any LOIs.
You will also want to make sure the LOI stage is marked as ready.