I would never to a remodel like this without plans. The process of drawing the plans will help you because it will make you think about each step before you get to it. It will also let the building department know if you know. Example: are your existing walls able to hold the new weight? do you need support posts in the garage with thicker concrete foundations? Every red line the building department puts on your set of plans will help you not make major mistakes that will cause you money and heartaches down the road. Even though the building department can be a big pain, they are a great source of information.