erick. A thought on your original post. Even if your windows are 2D flat squares make them coponents. That way you will be able to edit an entire buildings windows (or any other repetivly used geometry) by changing only one. Also, you can use simply constructed components as placemarkers for more elaboratly modeled versions. You can reload the fancy version when they are needed. This will save your CPU for zoom/pan/orbit while modeling the rest of your city.

Always always always model on layer0. Move only entire groups to a diferent layer. If you come from AutoCad forget everything you know about layers.