rootfs -- as far as I remember yes, if that 3.2.1 image is a specially-made image for DXG. To be honest the most recent DXG I've restored to the 2.5.8 rootfs, but all the previous ones *I think* I just rolled 3.2.1 rootfs onto. It's been a while ago tho, so if knc1 had a more recent experience with the custom 3.2.1 image, listen to him.
For the voltage -- everything I've used is in the photos. I didn't know it required level shifter, so I've used everything as pictured and (knock on wood) haven't fried a single DXG yet. YMMV of course.