grouchy old man couldn’t have said it better.
I am a beginner and my 2’ x 4’ space is large enough for me to learn the craft in. IMO you are starting too big.
Anyways, here are some rough factors for your consideration.
Lighting: assuming top line quantum board 30 watts/ft2
Yield if everything goes good 1 to 1.5 grams/ watt.
Ft2/plants varies with grow style, most recommend 4 ft2/plant. The number of plants has nothing to do with yield as long as you properly fill the area during veg.
So in your 8 x 12 tent, I would install 3000 watts of good quantum board lights and grow 25 plants. An experienced grower would yield at least 3000 grams per grow or 6.5 pounds. A beginner like me would be in over his head!
BTW, my light cost $50/ft2. So in your 8 x 12 tent you will spend most of your budget on lights. You will also need climate control equipment which isn’t cheap for such a large area.
Good Luck!