Try this post Memoization Policy with max history there are some in-depth answering on max history.
About the story management part:
If your planned action flow follows this Greet story, I would suggest you keep it this way. With augmentation-- 0, you can now add in other stories such as generic Intent-Utter pairs.
A story is your bot’s reply logic flow. If you wish to have greet to stay the same, just keep the Greet story under one.