In your case, you should set [font=courier new]serverUserPreferences[/font] to [font=courier new]null[/font].
User preferences on server side are useful to reduce the size of the saved SH3D file, by replacing the furniture and textures stored in a SH3D file by URLs if they exist in the preferences catalogs too. This is the case in [font=courier new]HomeTest.sh3d[/font] where you'll see that the size is smaller after the first call to [font=courier new]writeHomeEdits.jsp[/font], because it contains some furniture of the default catalogs (but also some furniture and textures not found in it). But keeping a larger SH3D file on the server is not an issue, it will be just more data to send to the client when reading the home it contains. Anyway, if the designed home is built from scratch on the server which is probably what you want to propose, the [font=courier new]Home.xml[/font] entry in its SH3D file will contain only URLs and will be as small as possible.