Only download BitGApps from official sources. Fake GApps packages are a common vector for malware.
Flashing after the first boot of the ROM often leads to Force Closes (FCs) and account sync errors, as the Google Services Framework must be installed before initial device setup. bitgapps-arm-12.0.0-r45
Installing BiTGApps is usually done via a custom recovery like : Boot to Recovery: Enter your device's custom recovery mode. Only download BitGApps from official sources