In the mean time I have done quite a lot of design work on the preferences dialog. I think I have arrived at a rather nice modular layout, whith which I will be able to present many settings without being too overwhelming.
Furthermore, each and every setting will have sensible default values so if the user ends up in a configuration mess, all he/she has to do is remove the gpredict.cfg file and restore everything to defaults. Tonight I finished a tab in the General preferences group concerning time and number formats. See the screenshot here: