What problems would there be if you fused with your sprite then flew all the way to your dream moon and killed your dreamself then put them on your sacrificial slab in the core of your dream moon? (Keep in mind, the dreamself is killed before taken to the slab)

Actually this is hard to say, because we have no instances of anyone drying on their Quest Slab while still having an iteration of themselves alive! Quest Beds have always been used when you have your body and Dream Self, and the Crypt Slabs have been used when there’s just the waking or the dream self left, with the other long dead. I’d imagine maybe you wouldn’t ascend? You’d need to carry the Dream Self over to your Quest Bed- Or would your Sprite self have to be the one to die on the Quest Bed? We have no precedent for these hypothetical scenarios sadly.