Windows doesn't like to be in the extended partition, so re-do the partitions so that Windows is on the primary partition. Linux can be anywhere on the hard drive. When you use Partition Magic, make a primary partition for Windows and an extended partition for LINUX. Don't format the extended partition using Partition Magic. After Partition Magic has finish, test if you can boot into Windows. If it works, make a boot disk for Windows and reboot the computer. Then run freebsd installation. Now you can make partitions for LINUX and format them. Partition Magic has its own way of formatting partitions, so its best to leave Linux filesystems to the native Linux utilities. Its ok for Partition Magic to format FAT32 and NTFS but not LINUX filesystems.
For the space, install only the packages that you want. 8 gigabytes is well over enough for /. My / is about 3 gigabytes, but /home (9 gigabytes) and /boot (16 megabytes) is not included. Those are on seperate partitions.
You could use parted to resize LINUX partitions.
BTW, try using df -h next time.