Im Using a Greenhouse for my Autoflowering...Questions

Im using a greenhouse for my autoflowering seeds. I was wondering whats an average size I should be looking at per plant?
I will be using a soil mix(if anyone has any suggestions on that you are welcome to reply).
Also I plan on growing some regular seeds but having them in same greenhouse, will this be a problem?

no it will not. If you have some well bred autos they can easily yield 1 plus oz, sometimes upwards of 2 if not more if you treat them well, give them plenty of light and keep them in larger pots. I use 5 gallon air pots and regularly pull at least 1 oz off each. Sometimes you just wind up with shitty phenos and get a 1/2 oz plant but in general they're good for 1 oz plus.

I use FF Ocean Forest, it works well.

Do you plan to run the lights on 20 plus hours a day or are you growing them 12/12? With the photo periods in there I'd suggest, if you have the space, keeping your lights on 20 plus hrs a day until the autos are done letting the photos veg out big time. After the autos are done flip to 12/12.

If you grow autos 12/12 from seed you're sacrificing max yield. Theres my 2 cents!