I have 2 in a 3x4 tent and its crowded.
Number of plants is not the way to think.
Depending on grow style you can do 1 or 12. But you will get approximately the same yield.
Lots of grow logs on the forum. Use the search feature and check them out.
And autos are unpredictable and may be small or huge. I had one auto grow over 6ft tall and fill my tent all by itself.