It sounds like you've got a good plan going. An often stated "number" for ventilation is 1-sqft of vent area per chicken. I'm roughly counting 7-sqft in the south and north windows and the gable vents. I'm not sure how much the soffit and ridge vents will add to this, but I think you'll be good with it. BUT, in the winter you will probably want to shut that north window will you not? But, with some good soffit vents I think you should be fine
An 8x8 run will get you by for a while as the chickens grow, expanding it as you mentioned will be great! The more space you can give your chickens the happier and healthier they will be!
It's looking good!
Ed