Ok, 80G ext3 sounds fair, and Id also use this drive to store all the data.
If you _must_ _have_ another external drive that has to be accesible from windows PCs, too, then do not format it with NTFS, but use FAT32 instead.
NTFS is really hideous on the slug and causes it to become unstable and constantly crashing.
Fat32 is well supported though, the only caveat is no files >2GB are possible.