Obese and trying to lose weight

I lasted weighed 356 lbs (July 2008). And as far as I know, I probably have gained more weight, since I stopped trying to do calorie restriction. So I plan to add regular fasting in my diet. 5-7 days bi-weekly. So, do I risk getting stretch marks and loose skin? My goal is 120-140lbs. I am dark, brown skinned, so if I have any current stretch marks, then I can't see them. But I'm sure they are visible in light. I plan to pursue a career in acting, so I'm trying to get my body in better shape.