ICloud – My icloud account was hacked, I changed the password, what else should I do

In any of the common scenarios in which you store your Store credentials on devices under the control of others, it makes good security sense to have those be different from the ones you use for iCloud.

For example, it is common to share music among family members by using an Apple ID for purchases on all of the family's machines. If that Apple ID were the same as the one you used for iCloud, then (unless you can be sure that all family members have secured their machines) anyone who got his hands on one of those machines could potentially gain access to your e-mail, calendar, and documents (and, in typical configurations, could even log on to your machine if he had access to it).

What is "Apple Persistent State Encryption"

Used by the persistent state feature to encrypt window snapshots to ensure privacy.

It is changed frequently.

So that one is normal.

As for your password, no one can change it without knowing the old password. If you have set up your log in with Apple ID assistance you can use it to recover your password. Read more here.