First, I would have a physical to make sure you are healthy enough to start an exercise program.
The one statement in your question that concerns me is the "get extreme in a few weeks". Being fit is not a short, one shot deal that you can accomplish in a couple of months and boom, everything is grand. It's a long (hopefully lifelong) process that builds upon itself. If you start out and then get extreme very quickly, then it's likely that you will either burn out or incur injury that returns you to the sedentary life.
I would recommend starting out by simply walking a few times a week, building up to where you can easily walk 30 minutes, 3-4 times a week. Add to this a weightlifting program such as Stronglifts 5x5.
Your abdominal muscles may get very fit, but you won't be able to see them until you lose the excess weight. That means that you also have to start paying attention to your diet, which is how much and what you eat.
You don't really need to buy anything, most of the resources you are going to need are available via web sources, and getting out and exercising costs nothing except maybe some gym fees.