No FFS can only handle partition sizes of just under 4GB with FASTATA. You need a file system like SmartFileSystem (the one I use), with SmartFilesystem I have varous sized partitons on my 2 500GB HDs and FASTATA, the biggest of which is 250GB, but there is no real limit on partition sizes using SFS and I have never lost even one bit of data in the years that I have been using it. 
Ummmmm no. I have only ever used the standard Amiga file system with FASTATA. It has no problems with partitions this size. especailly under os3.9.
There is a limit to filesizes of a couple of gig, cant remember the exact size. but your 80GB partition/drive should be fine.
You dont need SFS. Though it is a better file system
