Yeah you have the right idea but at 20 weeks your just possibly going to start seeing results. If I were you and looking for fat loss, I would run it at 4 iu's 5 on 2 off to stretch it out. In the meantime try and stock up on enough to run it 6 months or longer. This advice is coming from experience and years of research, not heresay.
Def, run T3 at 20-25mcg's a day.