Although it may not directly help with setting up your milestones, you would find ISO 9002:2016 very useful. It provides help in seeing how others have approached each of the requirements. It was written by the same group that wrote 9001. You would probably find it very insightful.
Also, if you are trying to show your customers that you are serious about getting certified, talk to your certification body. If you are already heading that way and you have a contract with them, most certification bodies will issue a letter of intent that often pleases your customers.