It depends on the size of pots you use. Considering the speed at which a harvest is produced - by going directly into bloom after your clones take root - your pots won't need to be larger than 4L - but don't go below 3L. By using square pots you'll be utilizing the space more efficiently. You could cram 36 15x15cm (3.4L) square pots in there with some wriggle room to spare.