2. It's mentioned that the Essaence is NOT the same as Arcane magic, but is this discussed formally somewhere I haven't looked yet? Before I'm ready to run in this world, I'd like the distinction nailed down pretty firmly, ie HOW is it different and what are the game effects of this difference?
Essaence is even more primal than Arcane. Essaence is the raw magical energy that is present on Kulthea. Arcane Magic is just an application of the use of that magical energy, as are the three other realms ( Essence, Channeling and Mentalism )
In game term, very few people understand truly Essaence, these few people have furthermore have to go though a long and difficult training to learn a few use of Essaence... Basically they are Loremasters and Navigators, and the extremely rare peoples that spend the time learning the spell lists Warding Lore and Warding Power.
So all in all, there's 14 Essaence spell lists, 6 are restricted to Loremasters, 6 are restricted to Navigators, the last two being quite difficult to learn about and even more difficult to learn.
3. Are the spell lists for the Loremasters and Navigators published anywhere? Perhaps in Powers Of... (which I don't have YET)?
To complete the answer, the Loremaster and Navigator lists were published in the Master Atlas World Guide ( Blue book from the Shadow Wortld Master Atlas Box )
The two Essaence Warding lists were published in the Shadow World Atlas Addendum ( pink book from Emer Box )
All were published again in SWMA 2nd Edition.
They are not in 3rd and 4th Edition.
4. Do any published materials indicate the architectural and/or aesthetic/artistic differences between the, for want of a better term, fore-runner cultures, such as the Althans, Worim, etc.? It'd be nice to know how they built when designing their ruins for hapless little players to die in.
The cover of the Emer Box is supposedly the City of the Dead. IIRC, of Jinteni making.
Otherwise sadly, there's not much left... several millenaries usually do that to
human ( or any other race ) made buildings.... and only things that were built with the will to have it stay for a very long time in a climate that allow it will have survived.
typically Egyptian Pyramids... In Egypt. The same pyramids in Europe would have been reduced to rubbles long ago ( too much rain, rain and sedimentary rocks usually ends up with erosion... fast erosion )