I finally managed to complete the update of my private website. The new site is not only better structured (at least in my opinion) but it now also is optimized for mobile devices such as mobile phones and tablets. A few places still need some polishing, but all in all, the update is ready.
That was about time, because on 31.12.2014, support for Joomla 2.5 ran out. I already set up a Joomla 3 -based site in summer 2014 to succeed my old Joomla 2.5 site but due to lots and lots of stuff in my calendar. I didn't have time to do the migration as fast as I would have liked to.