It can use USB-C flash drives. Not sure if it outputs enough power to spin up a hard drive on its own. You need to get a video player for the headset that knows what to do with external media, though. (Skybox and 4XVR do. Dunno about others.)...
Human reaction time is more than an order of magnitude greater than that. 12ms is well within your brain's ability to seamlessly compensate for.
There's plenty that makes me want to purchase it. Not $3500 of want, but there's some pretty cool...