I have 18 months--what would your strategy be?

I am going to turn 30 in 18 months. 

I want to dedicate these next 18 months to hitting 30 in the best shape of my life.

I’m 6’2” weigh about 255 lbs. 

As background, I’ve swung back and forth between being overweight and overeating and being in “okay” shape and eating generally healthy for most of my 20s. In college I would run and lift, but I (obviously) ate like garbage. Immediately after undergrad, I started law school which was a really challenging phase in my life emotionally and mentally and (despite occasional times when my activity/health would spike) I generally overate and didn’t exercise. Of course, after law school, studying for the bar and then practicing as a junior associate in large firms, I convinced myself I was too busy to devote any time to my health—any spare time I should be billing or spending with my wife. I got into the habit of not sleeping enough, eating whatever I wanted (because that’s one thing you can do when you’re stuck at a desk all day and night), drinking unhealthy amounts of caffeine and nicotine (Zyn pouches).

So yeah, sorry for rambling, but here I am. I’m 28. I’ve achieved some level of career success and I really do love my job. But I know that I am in bad shape and I want to do it for a long time without dying at my desk with a heart attack at 45. I have a bit more freedom with my time these days as I can delegate some of the grunt work to new juniors and I am better at predicting workflow so I want to take advantage of that. But I also know that things can change quickly. All it will take is the right client email to remove me from society for a week or two during which time I will abuse caffeine and nicotine, eat garbage, not sleep, and not really leave the house.

I want a plan, a set of achievable, progressive goals, that I can track as I move through this next 18 months to ultimately land at 30 with more energy, better health, more confidence, and a set of habits that I can remain dedicated to as I move into the next phase of my life. 

As for where I am physically—I can run for a few minutes before I’m winded. I can knock out a couple pushups. It's not great.

What would you do? How would you start if you were in my shoes? I feel like the time that I have to reach my goal is a long enough horizon that I can be strategic and smart.