Akatsukami has it right. Do you mean amount of space, or do you mean a minimum length logical record?
You can allocate a data set with no tracks. Obviously you cannot store any data in such a data set, but you can allocate it.
The FB or VB issue depends on what you plan to put into the data set. Many programmers are uncomfortable using data sets with varying length records, but I've been doing this for close to 40 years so it's second nature to me.
One not so obvious issue might be what is the minimum block size? I would advise 18 bytes, which might also be advisable for a minimum logical record length. The reason for this is on magnetic tapes a record that is less than 18 bytes, and if it is read in error, the record would considered noise and simply discarded without attempting to reread the record or notifying your program. I don't know if this is still true with modern tape drives, but it was certainly true many years ago.