I believe where we landed on this was that if you are trying to bring a device from an unsupervised to a supervised state, restore from backup will not work at initial setup (either from itunes or icloud). Our recommended method would be to have your users sync any app data in icloud, and then login and re-download that app data from icloud once setup is complete (this can't be done in the "restore from backup" step in initial setup). I would probably suggest skipping that step (you can take it out of the setup process by selecting it in "skip steps" when applying DEP settings).
Note - if you were *just* enrolling the device in DEP and not supervising it, it sounds like restore from backup would work at initial setup.
With regard to the wifi profile disappearing once it's enrolled - I believe what's happening is once you have configured the Meraki Management Profile (SM), any previous profiles will be removed. To configure a wifi profile with Systems Manager, you can set one up in the Systems Manager>Settings page. Here's more on that - https://documentation.meraki.com/SM/Profiles_and_Settings/Configuration_Settings
I'm not sure why you're not able to access user account settings - do you mean the user is no longer logged in (to icloud?) or that logging in to icloud is blocked? There is a restriction you can set to block this - in SM it is under Settings>Restrictions>Allow Modifying Account Settings. If this was unchecked, that would block a user from signing in to icloud.
Hope this helps!
