Sorry it took a while to reply. In answer to your questions:
1) Have a small/medium map each for the clan camps. (Along with one for the moonpool/mothermouth area).
2) It seems the link has been taken down since I last downloaded it, so pretty much any den meshes (though preferably not the games original ones) will be fine.
3) Any of the wombat packs, for animals, and there is one for plants and rocks too. You can find them here:
http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=11142.04) As long as there is a variety of trees, I don't mind too much and WoW meshes are great.
5) Try and have it so that a lot of the area is forest (preferably oak one side, pine the other) but with quick changes to swampy areas (e.g. around the river) and mountains found in certain regions of the map with more rocky areas and so on (as much of a variety of different locations and scenery as possible). Loner dens spotted around sound great, possible the odd larger den for rogue groups or a house or two for kittypets. Training hollow would be best in the separate camp maps.
6) Either, however I don't use the forum a lot, so it might be better on dA (I'm also known as Skylandy on there).
As for the 'quick changes' to the surroundings: Try to have lots of different areas to the map, shown through terrain, vegetation and mesh changes along with maybe changes to the height. For example, the mountain areas would be higher than the forest areas and will have different meshes and terrains to make it more rocky/cliff-like in appearance. Clearings would be more open than the forests, surrounded by trees and bushes and with a lighter grass terrain texture and more flowers than usual and slightly less larger bushes. However, so as to fit it all in, try to make these particular areas very small and change from clearing to forest area quickly. Forest however would make up the most of the map.