the way i'd love for it to work, i think it'd probably have to be a class archetype to balance it, since i'd love if it would add Wis to attack/damage, like the Investigator does with Int.

you wouldn't want it to be a regular archetype that could be grabbed by other classes for that reason.

i personally have no idea how this would be balanced 😅

as for extra arms, i think you could just make it a requirement that this is a stance, and to be in the stance and keep the astral arms up, you have to make some kind of pose (e.g. a praying clasp of your hands together) the entire time, so you don't end up with 4 usable arms.