Re: multiple volume archive
The basic tar command is :
tar -c -M -f /dev/fd0 files-to-tar
or more obvious: tar --create --multi-volume --file=/dev/fd0 files-to-tar.
-f or --file tells tar which archive to read or write.
From a cursory perusal of the info manual, it doesn't appear that you can specify the size. With -M it justs writes until it runs out of space and then prompts for a new floppy.
The 'split' command will divide a file into whatever size chunks you like.
Check the info manual (not the man pages) for tar (look for 'Using Multiple Tapes' section) and the info manual for split.
Post again if you need clarification.