Is there a non-physical free will zone or dimension out there also which spirit meddlers can inhabit? Maybe like the lower astral?

This, in fact, is their environment already. They live within the lower astral which extends throughout your galaxy so they will be moving in a free-range fashion among worlds depending on their energy levels and intent. They are not able to reach the higher planes unless escorted with permission by the divine realm and its representatives. Other dimensions are off-limits to them in a similar fashion.