Have dedicated servers.
By your description, large, medium complexity clan builds would be a good start.
Cities work well, build roads and buildings within a 32x32 grid is not that complex, (as apposed to curvy roads etc.) people can build within good detail, and the end result is impressive.
Terrain, similar to Badspot's river builds would be fine, and with that you can aim for many different styles, if you want your clan to be a particular style.