a puzzle about spirits

[whswhs]

I'm looking at starting up a fantasy campaign in a few months, where some of the player characters are likely to be spirits living and acting in the spirit plane. Now, I understand how the spirit form meta-trait works. But that's for spirits that have come from the spirit plane to the material plane, where on the one hand they are invisible, intangible, and (in some versions) inaudible—basically just floating points of view, and on the other hand they are exempt from all metabolic needs. But that's not necessarily true on the spirit plane, in either case. Everything there is a spirit, or made of whatever "stuff" spirits are made of, and presumably spirits have some sort of life-sustaining interaction that's functionally equivalent to eating, drinking, and breathing, in the same way that a machine has a need for fuel.

(i) What is the proper representation for a spirit residing in the spirit plane?

(ii) What is the proper way to define the trait "able to visit the material plane and travel about there as an invisible, intangible being"?

Also, there will probably be human characters visiting the spirit plane, whether in dreams, in trance, via spells that produce the same effect, via spells that transpose their bodies there, or via gates or "soft places" that let them walk from the material world to the spirit plane. How does one represent a material being visiting the spirit plane, from the viewpoint of the spirit plane?

I'm getting a bit stumped by this. But it seems to me there out to be a way to define all this under the RaW that I'm just not seeing.

Bill Stoddard