A: Yes. The survival script preserves Gapps during dirty flashes. After OTA, reflash TTA Gapps just in case.
: The essential background framework that allows apps to communicate with Google. Google Services Framework : Manages account synchronization and cloud messaging. Google Play Store
However, the success of the installation can also depend on the custom ROM being used, as some ROMs may have certain limitations or configurations that affect the installation process.
