That might be a little small for outdoor. One important thing about an auto, is that you want to start it in its final pot. Transplanting stunts them too much. With a normal flowering cycle type plant you are right though. You would not normally want to start in a large "final" pot size. So for a final pot and outdoors, you would be better off getting some 5 gallon buckets at lowes, then using those. the square pots help increase the amount of soil you can fit into a smaller grow space...But that is not important for you, so really the bigger the better. You would be surprised how much dehydration there can be in a day with outdoor potted plants.