It's easier than you think. I use clear garbage bags (so you can see-through). Turn them upside down, cut a small hole in the middle. Take Movi off the Ring, put the Toad in the Hole through the hole in the bag, re-attach Movi to Ring. The bag hangs down like a skirt over the Movi (and camera) and doesn't really interfere with the operation. The Ring is exposed to the Rain, and so is the top of the Toad in the Hole. If you have a clip-on matte box, you can tuck the plastic in to that to keep it out of the way of the lens. I recommend using two bags, in case one leaks. You also need to rain-protect your on-board monitor, and I use the clear plastic for this, too.
That's more than what we even do. We do a smaller clear bag for just the camera and then saran wrap or a small ziplock bag for the brain of the movi.
No. Same as on drones, the motors are pretty resilient to water. At the end of the day make sure to put the movi somewhere that it can dry out properly though.