15' x 7' x 7' Greenhouse for Autos?? (SW Mich)

So im thinking of doing mostly autos in this 15x7x7 greenhouse im looking to pick up. Was originally looking at a 20' x 12' x 10' to grow everything in (photos & autos) but im thinking that's just a bit big for "personal use" growing.

Never grown autos but got a deal on some seeds, so I've picked up a few strains. Is 4sq ft per plant sufficient?? I'll be doing 5gal fabric pots with FFOF.

Im thinking I could get 2 harvests of autos in over spring/summer, then move my photo plants in it come late flower to keep moisture/dew off and extend our Michigan flowering season

Thoughts?

4 square ft. isn't much space it will be awful crowded. I keep 5'-6' between my out door plants.

Hmmm 2 auto harvests and a photo harvest for personal use ... you must have really high tolerance
But seriously ... what autos are you planning? You're going to have limited light outdoors considering that they like 18/6 indoors so you might want to go with 8-9 week strains rather than 10-12 week strains since you'll probably have to extend them a bit for better potency. I'd allow at least 9 sq' not 4. They're autos, but plants that are supposed to reach 40-50 inches are going to need elbow room or you'll end up with a greenhouse full of PM and bud rot. That will still give you 8 plants with a little space to move around between them for maintenance.
As for moving your outdoor photos ... what size containers are you using? I grow photos outdoors in the northeast in 50-60 gallon fabric pots ... they don't move!

Currently picked up Lowryder Auto and Blue Cheese Auto. Planning on growing in 5gal fabric pots and both strains are ultra short stature and finishing time. The photo strains I have planned are Critical, Gelato, and Pineapple Express. I try to keep everything in 5 gal pots to keep things smaller