[crunch]

@1) Most boards use a 'simple patch mesh' found in your curves menu on the tool bar, or separate patches of LOD terrain for larger areas of rubble. I don't offhand remember the exact texture, but I know there are a few that look like destroyed piles of rubble. There are also rubble piles in your static>obstacle menu.

@2) Easiest way to make non-entered buildings is to create them out of a few solid brushes made of caulk, and then texture the outside visible faces.
If you type "wall" in the texture bar (that empty white space under your toolbar) all the wall textures will come up, including those with predrawn no-vis windows.

@3&4) I have yet to start working with AI, and cannot help.

@5) I am not a great scripter and can only use minor scripted events. Vonderbakluft should be able to help you if you post your question in the scripting section of Nemesis' forum.

@6) You can manipulate all your terrain in Radiant. With your terrain selected, hit "V". Pink dots that represent your vertices will show up. You can manipulate them up and down (ONLY up and down) to form hills and craters. Beware that once you adjust your terrain, if any vertex of your terrain is higher than any solid brush in your map, you will not be able to use CSG subtract anymore! It will cause a shutdown. Also, if your terrain intersects any solid brush, the same will happen.
I have found that importing terrain does not work as well as creating your terrain directly in Radiant, but that's just my opinion. Also, I usually don't put any terrain into my maps until almost all of my construction is done.

Happy Mapping! Kill Ya Later!