If you would, I'd like to be educated on this difference you've suggested: the Tome has no writings on such, and it is certainly an important aspect of time research.
As for the "other forces", I am well aware of that fact, but such forces would be incredibly unwise, indeed, foolish, to attempt using this ritual to do so. Nothing can be brought back that wasn't brought along excluding memory, and furthermore, the ritual only provides protection from the forces within the Astral Plane. It is not the same as a planar asylum: any non-creation magic will be utterly useless there, fizzling the moment it is cast, as a result of the order of Universal Components. Even the Outcast would be unable to use magic there, and any being who CAN use pure creation magic would obviously need no help of mine to reach the astral plane. They could simply rift there on their own accord.
Other than the benefits I have described, such as knowledge and the likelihood of a spirit forge-like effect, there is no physical or magical power to be gained from this venture. It is merely a chance to find out the truth behind Magic itself and the force(s) that created it, if such a thing exists. This is my goal, along with the chance to find my Adoptive mother, the fey Flidia, who disappeared 204 years ago. The ritual will bring the five straight to the source of creation magic, which my research points strongly indicates as the being called "the World Dragon". He would be able to tell me where Flidia is or what happened to her, seeing as no one in the last two centuries could, not even the fey themselves.
As for your question about additional requirements, it largely depends. Matter, Spirit, Magic, Time, and Space are the five roles, or Seekers, that must be present in order to perform the ritual. Each of these has it's own nuances. As a side note, and I'm sure you wonder this, as well, it has foundation in Celestial Magic. Not by nature, which is really indiscernible, as the ritual itself is not too much newer than dragon magic rituals, but during the course of the ritual, a prison spell is cast on all five Seekers.
- Wycliff, the Seeker.