Unzip content cd to the directory where you want it. Adding things to the internal browsers requires using the little icons at top right of browser and selecting the folder to add. Not sure specifically about terrains. I am assuming it converted it to an object. My guess from your description may be that you should make sure your group is closed in the tree before selecting the entire grp. I would recommend taking the tour of the interface tho. You could be using the wrong tool. Sounds like you are moving in or out via camera or you are doing that to the terrain. Fire may not do what you want, but you may want to look at primivol plugin for more options. There are ways to simulate looks tho. Toon pro lets you mix and match some, I don't think noir will (just post process effect) and agoos is not for rendering it is a shader option. Depending on what look you may need to post process.

Oh forgot your other stuff. Yes you can customize skys many ways. Turning the ground off for the sky requires unchecking the little box listed there on the general tab to the top right.

No need to think outside the box....
    Just make it invisible.