1. If you flash gpe rom, your system files would be modified. You will further not receive any updates from Motorola moto G but will be eligible for updates from Google GPE.
2.Definitely yes, flashing a rom modifies only software not hardware so as soon as you will be back to stock moto OS, the moto apps will start supporting your device and most probably your rom.
3. You may be able to relock your boot loader but your warranty will be void. Whenever anyone unlock its boot loader it communicates with moto site to get unlock key and at very time loses its warranty.
You can try that method but maintain all precautions and do have a backup.
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