I don't have any medical knowledge of how to go about this, but I will say that personally, when I added High Intensity Interval Training, that really made a big difference. I would say that after you are doing what you're doing for 2 weeks, you should add the HIIT to your routine. In case you don't already know, what you do is just when you are walking, every 3 minutes, you would run as fast as you can for about 30 or 45 seconds. I'm talking full force sprinting. Then, you walk for another 3 minutes or so. Make sure your heartrate goes back down to a slower pace or this will not give you the benefits of HIIT. I've read in Women's Health and Oprah magazines that people who do this type of workout burn 3 times more fat than those who workout at a high intensity the entire time. Raising and dropping your heart rate will release something in your body that makes you lose more weight.
I'd definitely warm up for 5 minutes and not do this for more than 30 minutes total...you could walk for the rest of the time you want to do cardio (or go back to the walk/job combo). Also, when you're just walking, maybe you could mix it up by doing lunges, squats and push-ups in the middle. That will also add a little something extra to the mix. I think it is SO important to keep your body guessing.
Once you're doing this for a while, maybe on the days that you climb stairs, you could do more stairs and then, walk every other stair and then ever stair for each flight you alternate how you do it. KWIM?
First goal: under 180:
Second goal: 175 or below:
Third goal: 168 (no longer overweight):
Fourth goal: 160 or below:
Final goal: 145-155 (not sure if this will ever happen):