Why not make the easiest changes first? I was once close to the same weight you are, and I don't think I've ever really counted calories, for example.
If you drink regular sodas, you could substitute water. If you eat a lot of junk food, you can limit it to only the weekends. Go for a walk every morning. Start doing some body weight exercises a couple of days a week. Stuff like that.
Although I'm not qualified to comment on it, I suspect the mental health issues are going to be what really needs to be dealt with in the end.