I went to the recovery and formatted the data partition, this gave me pretty much everything back. I know have the whole sdcard partition back (25.2 gB out of 26 gB, I am guessing the other 6 gB go to the system), but still can not access it from the phone, only from the recovery panel.
Yea the rest of the 6gb does go to the system itself. Just like on the 16gb version which most have there's around 11gb available even before installing a rom
From my Wicked S3 running MIUI