There are simply too many variables to really give you a concrete answer. Strain, training methods, and length of veg time can make the answer be a little as 2 or as large as 16 or more if sogging.
I have a 20 sq ft space and feel that 8 is the max number that fit in there without becoming overcrowded....and even then, they sometimes do. But I like to let my plants get some size to them before I flip. It is a lot easier for this old lady to take care of 8 plants than 20 or 30. You will be able to fit more indicas than sativas. However, for a general answer without knowing a lot more about the variables, I'm pretty much thinking the same as pcduck--5-6 plants would probably be great.