Sorry mate but once again your wrong on OS3.1, 3.5 & 3.9 and SFS with SF2 partitions you can indeed read and write files even with the c: command "Copy"... 
Yes that might work indeed. It is not intended behaviour though. Just side effect of Copy command implementation.
Again I assure you in all the years of using SFS I have not lost one bit of data and applications don't handle the actual data transfer (that's what the file system does)... 
You can. I dont know if it was fixed in OS3 version but there was a bug it could accidentally trash fs admin blocks. Not so annoying than crashing FFS partition though.
The only problems you will encounter are application displaying the wrong file size as most were written never expecting to take files of >4GB into account... 
OS3 applications can never display file size correctly. It just isnt possible.
Heck even OS4.0 came with it's own PPC version of SFS as most apps in that are written to display the correct file and HD size... 
I have never seen it so cant comment.
As I've said before don't knock it till you try it... 
I have been using SFS since version 1.52 from 1998 and all my partitions are SFS still. Wrote small app for it long ago. I never had PFS.