Unfortunately the Moto G still a phone. It can still make emergency (911) calls without a SIM card. There's no way to disable that functionality, even in the various Android distros.

You can turn off radio by going into an airplane mode, then enabling Wi-fi. At least that's how I use my Galaxy Nexus as a media player after I got my Nexus 5. (and same method works for Nexus 5, so I'm assuming it'd also work on Moto G...)

You can disable the dialer and lock screen (or use a lock screen replacement from the Play Store).

I have never encountered a lock screen replacement that actually replaced the lock screen. I've seen some that run in front of it, but every time they'd just pass off to the real thing.

Disabling the dialer does not disable emergency dialing as far as I could tell.

The only way to dial emergency numbers is through the dialer or the lock screen. If you disable both then you can't dial emergency numbers. Then, if you still want to lock your screen you can use a third-party app.

You could see 911 calls as a feature. What if you are knocked unconscious and your kid has to dial 911? the new 'remote' could be a bonus emergency phone.