depends if your scroging or going for weight er plant. If you have a small aeroponics set up and keep veg short u can do like 16 or so but if you wanna veg longer deal with less plants and get same weight i would go for like 8 at most. Also depends if you have resivors or what because they take up space:/
You might want to scrog though because you only have a 6 ft ceiling.
focus on enviroment (how are you going to light it, air cicurlation, heat issues,) then think about maximiseing that space. If i srank my room
to ony what i needed(8x6X would be cramped but could do 60