Can you long rest during Astral Projection?
The implications of this are that you can simply astral project, travel through the Ethereal Plane back to the Material Plane through the Silver Color Pool as if it were a foreign plane, and then live out your life as an immortal with your body in a closet somewhere safe.
Without the ability to long rest, eventually your ability resources would run out, so you'd have to drop Astral Projection, get some rest, and then recast the spell with its costly components.
Similarly, if you can't long rest during Astral Projection, can you short rest?
The above would now apply, but to Warlocks and Monks exclusively as their ability resources are refunded on short rests. The difference being they would never regain hit die and there are some daily resources for Warlocks which aren't reclaimed.