Seems OK disk space wise.
Try formatting the whole lot as / to remove any partition size problems. If it proceeds past the install point from here, you can complete the install, then figure out how much space has been used with:
du -sk /var
du -sk /usr
du -sk /home
du -sk /boot
That should give you the relevant figures to find out how much kb are used in each area. Subtract the /var, /usr, /home & /boot number from the df -k value to find the space used by root.
As a guide, I've got a fairly comprehensive F11 install in a KVM guest with a 10Gb virtual disk. There's still 5.5Gb free on root.