Atlas questions from a TGE user

I've considered switching from TGE to TGEA, but I have a few hard questions first. There is nothing really specific on Atlas that is not locked away in the TGEA only areas and this Schrodinger' Cat approach of buy TGEA to see if I wanted to buy it in the first place is something I'm not willing to do. If someone can answer my Atlas questions, I'd appreciate it. From non GG sources, I seem to find that Atlas has two kinds of terrains; Unique and Blended. From what I understand, using the blended terrain is similar to the legacy terrain pipeline wise, except that I can import the terrain directly from L3DT, it is paged and am limited to 4 textures.

What is a "Unique" and how does it differ from the legacy terrain?

Does unique terrain use a single gigantic mesh + texture?

If I alpha splat a zillion channels in L3DT, can I bring that over to Atlas as a texture?

What is the main art pipeline for creating unique terrain textures?

How is the scene graph arranged with Atlas? I presume that the whole terrain is still loaded into the server scene graph at one time. How is it "paged" to the client and what is the network traffic impact of large terrains?

If two players are in the same zone and are far away from one another (no LOS), do they still register on each others' client scene graphs?

Caves, Dungeons and other underground structures. I'm building an RPG and an important part of that is players poking their heads into holes in the ground. Are these seamless as in Atlas as they are in Geo or do you have to zone? It is important to me that players can enter the cave in the mountainside and not zone and if this can't be done, then Atlas < Geo.