First and foremost you have to develop a plan that you feel you will be able to stick with, in terms of time working out , or time spent on/away from the computer. You want to avoid pushing yourself too hard right away and risk failing at it and then ultimately giving up. I know this sounds stupid (I can do anything I put my mind to), but making lifestyle changes takes time and in my opinion it's much easier and more effective over the long term to slowly add in new and more healthy lifestyle habits. You're not going on a diet, your changing your life. Sounds like you have your mind in the right place, just write a good plan and do your best to stick to it. If you fall off, the the f*** back on. Best of luck! You will have to post about your progress in later months to come.