The limit in jk3 to use the model as the func_door, rotating and other stuff is 1000 polys. I know there are some models in Jk that have more than that but it is not good for Jk :/ You should make Your model less detail. Make the windows as a texture same to the whole doors. The models in jk3 are simple and textures make them look detail. I dunno about sketchup. But i think You should use gmax or blender for this. I use blender and i recommend this program but what can i say ... My program my choice (before You make a model check if there are any exporters and importers because there could be issues on the way)