Moreover, there is neither precedence nor basis for astral projection using the force. If you consider that the force is supposed to be a "a force that binds all living things together", it becomes reasonable to move things using that force or to have great physical abilities, but there is no basis for astral projection
If there were, everyone knows an astral projection can only fight another astral projection.
If he went to sleep, “dreamt “ he was at a familiar place near nephew, then physically woke up in that place—I would buy it. Mass=energy, transforming dream state into physical, ie using his dream/astral/energy body to actually travel through space. There isn’t precedent in the earlier films, but there doesn’t have to be—it just has to make sense in a metaphorical way, and have some connection with either mysticism/religion, physics, or lucasian meta-physics. To not introduce new Jedi abilities would just be boring, especially since he has spent 2 decades learning(presumably) to unlock some portion of the milennia of Jedi knowledge. A hundred movies wouldn’t be enough to show every “trick” or skill the Jedi’s would have acquired.
Luke’s (or anyone’s)mass/material form body can’t be in 2 places at once; defies logic, ancient sorcery and physics. I’m sure that is why Mark Hamill objected to the script. He was thinking “why in the hell would Luke burn up so much energy(to the point of self destruction) to create a physical replica of his body light years away when he could easily use his energy body to travel, then revert to his mass/matter body for the battle?” (This follows some teaching of ancient Hindu mysticism). A battle he is sure to have won. Kylo has no lightsaber skills whatsoever, since Rey beat him in A force awakens, hell even Finn landed a blow, which would have embarrassed his grandfather to death! Sounds like a cheap, awkward, contrived plot device to kill off Luke. Ben killed Maul, Ben beat the hell out of Anakin, Vader killed old Ben, Luke beat Vader. Luke couldn’t lose to Kylo with both hands tied together. Hence stupid plot device. But writer(s) forgot that Star Wars has always been a fantasy that made sense. At least to me it did. Until now.