I don't think there is anything wrong with your setup. This is a property of Destiny (and Halo, for example). It's maximum turn speed is slow compared to CoD and BF. The best thing to do is try to best match your physical mouse movement to that of the maximum reticle speed on screen.
I'm not sure -- USB is a complicated protocol that requires everything on the bus to behavior according to spec. If one device doesn't do that, it could disrupt or bring down other connected devices. If your G13 is causing USB errors it could conceivably make it so that your XIM4 can't communicate correctly with your DS4.
Thanks for following up. The fact that it happened prior to the patch (even though less) is still an issue. You should never have disconnects under any circumstances. For example, we can run for days on PS4 without disconnects.
We've actually been considering including a high-quality cable in the box since this issue hits a lot of PS4 owners.