With those goals, I think I'd do something roughly like:
1. Pick if you want to start with diet or exercise. Exercise is a bigger boost to your overall health, diet is better for weight loss. I'd make the case for exercise first, because you'll have more leeway when you start on the diet part of the project. Whether you work on cardio first or strength first is also a matter of preference.
2. Pick a cardio exercise you like. Mustachian options are walking, running, biking, swimming. Do it 3x per week until it is a habit and easy. Start with 20 minutes a session and build to 40-50 minutes. Bam, you're meeting the recommended 150 minutes per week of aerobic activity.
3. Pick a strength program that seems doable. I also like darebee.com, but New Rules of Lifting is a great series too. Add 3 days of strength to your 3 days of cardio. Do it until it is a habit and you start seeing results.
4. Keep doing your exercise, and start writing down everything you eat. Do this until it is habit. If you lose weight just by keeping a food diary, keep at it until your weight loss slows, and then move on to the next step.
5. Cut your caloric intake by 500 calories per day, using your food diary as a tool. See how you feel and how your weight loss is. Do this until your weight loss slows, then reevalute your caloric needs as mentioned by a previous poster. Now you have the basics of a fitness and weight loss plan in place.
6. Progress your exercise in some way - step up cardio intensity, add intervals, lift heavier weights. Keep adjusting this ad infinitum to meet your needs over the years.
7. Fine tune your diet in whatever way it needed to reach your goal weight. Track your macros, cut carbs, eat more protein, etc. Whatever you find works for you. By this time you should have a pretty good sense for how all your tracked food affects your weight loss, so just continually make adjustments until you are reaching your goals.
8. Keep doing the food diary and workout plan forever.
This plan sort of assumes you start off needing a Dave Ramsey approach, and by the end you're more of a Boglehead or Mustachian. As you work at it more, you learn more, and you become more self-directed and able to adjust on your own.
Assuming you go with your plan of Whole 30 and P90X, I'd consider starting with P90, which is less intense than P90X. You can get all of the programs with Beachbody on Demand. All the P90 programs will give you results, so I'd progress through the original intensity levels even though everyone starts with P90X these days. And if you don't mind a program aimed a women to get a little less intensity, you can start with Jillian Michaels Beginner Shred, then progress to the regular 30 Day Shred, then start P90 if you want to ease in and build a little more slowly.
Good luck. I find fitness and weight loss substantially harder to keep up than good money habits.