It seems that the place is a sort of "blank canvas"/blank dimension, with similarities to TAR, but TAR is a specific dimension with boundaries and with many rules set in place by the Creator, whereas I think the "skimming dimension" is most likely an outlying layer of the pattern and empty. The possibility to "create" out of thin air exists in there (and suggests in turn the whole Pattern exists by the combined will of the Creator and the souls), but you'd probably need a massive strength of will and power of concentration/intelligence to form much beyond a platform. I doubt anyone but the Creator could turn this dimension into a "world" for example. TAR looks easier to change, as it's malleable by nature and you bend to your will something which already exists, it's not the same effort of will as creating from pure void.

And I agree with your explanation about falling. I would assume you don't really fall, the illusion of falling ceases once you stop to think you're falling, and you're just kind of suspended in the void. A channelller who is momentarily distracted and falls can probably stop the fall by creating a new platform and concentrating again on the destination. There's likely no way out of there for a non-channeller (for the same reasons there seems to be no way to enter TAR in the flesh except through a gateway made with the power, but that's not fully certain, I guess. I would still assume if a non-channeller "falls", he/she eventually dies of thirst rather than ever hitting any bottom.