Set the aspect ratio to 4:3, as that is closer to the sensor's native aspect ratio, and you'll effectively have higher resolution images as an output.
You should likely pick a framing guide, they're incredibly helpful to get framing and composition right.
DNGs are not shared, they're simply a RAW archival copy for advanced editing. If you have the storage space to spare, keep that on.
I rather like living images, I keep that on.