Personally i dont think organic makes a difference in soil...what id watch out for are any soil blends that say there soil contains 'time release nutrients' or anything to that effect. Anything from 'Sunshine mix #4' to 'Fox far ocean forest' to 'Happy frog potting soil' to Roots organics ... there are TONS of good potting soils out there.

One of the ezest ways iv found to hang mylar is to mount it onto cardboard using duct tape. you want it to be as wrinkle free as possible! i usually make 4 card board walls and mylar each wall and then lean them up against each other ...seems to work out better then just hanging the mylar on the sheet rock walls using tacks or w/e