Referring to your questions:
1. the keyboard only “learns” from you. You can add your words, phases to personal dictionary. Please read this guide: http://motoeguide.com/moto-e-guides/use-moto-e-keyboard/ (it was written for Moto E, but it also applies to Moto G and Moto X)
You can also turn on personalized suggestions. There are some other settings in Google keyboard to make your life easier.
2. You can always disable app update. Open Play store app, tap menu key (3 vertical dots in top left), tap settings, uncheck Notifications, Choose “Do not auto-update apps” for Auto-update apps.
3. It will occupy the storage temporally. The system will clear it later automatically.
4. Press and hold the Power button for 7 – 10 seconds, Moto G will restart. Rebooting is not a menu option in Moto G, but you can still do it.
5. The location service is needed for Google and other apps to provide location based services, e.g., maps and navigation.
You’d better turn it on and choose battery saving mode.
6. screen protector is not a requirement. Gorilla glass can provide good protection from scratch. But it is not scratch-proof. Sand, sometime, your keys, may leave some scratch on it.
Most people put screen protector on the phone to keep it “new”.
It is up to you.