Dial 1155 for balance. It will probably be in German though, although if you are lucky you may get an SMS (some operators do this, though I am not familiar with MedionMobile)
Not sure about the rest, but I'll take a look... or maybe someone else will beat me to an answer for you!
HAve a look at
http://www.medionmobile.de/konfiguration_iframe.php though yor phone is not listed there!