You should prioritize a healthy diet over exercise, but exercising is still very important! You should avoid all types of sugary drinks and only limit yourself to water. An ideal diet would consist of lots of greens and lean meats, Fish/Chicken/etc.
As for your exercise routine, walking is a GREAT way to start off, but maybe after the second week you can try jogging the 2 miles, and then once your comfortable with a light jog, try upping up to a run! And if your doing sit ups to try and lose a gut, then go on right ahead and do those sit ups! But if your doing sit ups just to try and lose weight, might I suggest you go for another run instead of those 50 situps, although both would be even better! Running and walking is by far the best way to lose weight as exercising goes, you should be losing weight all over your body through running.
I've been trying to get in shape recently too and I've stuck with a vigorous diet and a consistent jogging routine, and I got to say it's hard to stay consistent, but you gotta stay head strong! You can do it! Best of luck.
