**Edited after rereading your set upMy thinking was to start with autos as the ruderalis makes them quite hardy I believe and they tend to grow smaller. Plus I can have the same light setup and cycle for the entire grow. Also don't need a big yield but thought with autos I could get a different strain grown every few months. I like some variety. Will definitely do a photo grow at some point though. Hoping to have many happy years of learning ahead.
I think it depends on the autos - I have GDP blast autos that are very squat and that are... quickly pops out to measure... 190mm/ 7.5" (well trained). One of these would fit into your box
I also have northern lights blue glue autos and they wont stop going out and up. One of these would not fit unless trimmed repeatedly.
Lots of experienced members reading your post by the way (this doesn't include me, I'm a total newb!) - if you are thinking soil and organics, even just for good watering practices look at some of Emilya's links and posts.
Good luck with this,m I'm watching with interest - oh and watch out posting pics with the LEDs on... it seems to send people nuts!