For an example, my 1.5TB HDD has 3 partitions:
1GB FAT -> 500GB WBFS -> 900GB NTFS
FAT Partition is used for my loader and the cover art (Configurable USB Loader)
WBFS Partition is used for the disc images (cISO files)
NTFS Partition is used for other media, like music and movies (Videos with GeeXBox and audio with DMP)
I have found that games are about 2-3gb each, as an average... (Wii Sports is very very small as opposed to SSBB which is very large) I currently have about 90 games on my 500gb partition and am no where near filling it up.
I'd also agree with the poster above me, use WBFS Manager 3.0, should work out for you very well.