Grow Room size vs number of plants

I'm new to indoor gardening, and am planning out my grow room before I get started. This is a personal use project, so I don't need 100 plants or anything crazy like that. But I'm not sure how many plants I can fit in an area, and was hoping to find some help here. My plan as of now is to close in and insulate an area in my attic. I'm thinking 5'w x 7'l, with a ceiling height sloping from 7' to 5' long ways.

I want to split it into 2 separate sections for veg and flowering. I'm not sure if this spacing will be ideal, or if I should try to section off more space. I do have more space available, but I'm concerned about needlessly raising heating and cooling costs if I go bigger than needed. About how many plants should I be able to comfortably fit in this spacing? I plan to grow in soil, and would like to keep 1 or 2 mother plants so that I don't have to continuously order seeds.

I'm at least a few months away from actually building this. I really appreciate any help you're able to offer based on your experience.
 
Top