The bulk of the output will be in the form of tables where each row describes one client. Here are some general design principles for Web-based tables:
Columns should be as narrow as possible so as to present the maximum information without requiring noxious horizontal scrolling. However, they should not be too narrow if it obscures the meaning.
Column heads must also be narrow, but not too narrow to make sense.
More important columns should be further to the left, in case the table doesn't all fit on the screen.
If a column may become large, it should move further to the right, especially if it's not one of the more important fields.