Question 1: Yes, The SDK generates a unique visitor ID when an app is installed. This app visitor ID is stored within persistent memory on the mobile device and is sent with every hit. The app visitor ID is removed only when the user uninstalls the app (app visitor IDs persist through upgrades).
Question 2: It is same as VID or any other ID on web, though no third party advertiser can use it to track/show ads on user device. However I would suggest to reachout to Adobe Client Care for confirmation.
Question 3: You can try using Adobe Mobile Services to show interstitials and track users opt in/out status. Starting with iOS SDK 4.8.5, privacy settings set via the setPrivacyStatus method affect activity from Analytics, Target, and Audience Manager.
Note:ADBMobile JSON config "privacyDefault" setting is Default: optedin
ADBMobilePrivacyStatusOptIn - hits are sent immediately.
ADBMobilePrivacyStatusOptOut - hits are discarded.
ADBMobilePrivacyStatusUnknown - If offline tracking is enabled, hits are saved until the privacy status changes to opt-in (then hits are sent) or opt-out (then hits are discarded). If offline tracking is not enabled, hits are discarded until the privacy status changes to opt in.