Start with Your Health First
Your health will determine your ability to succeed in every other area of life.

Without a healthy and energetic body, you will never be able to succeed at the highest levels.
Your ADHD brain needs to be operating at maximum efficiency. To do that it must be supported by a high-energy, healthy body.
Set a goal, over the next two years, you are going to gradually work to
Exercise 4–5 times a week, preferably doing something you enjoy
Eat a whole food diet and reduce buying food from major corporations with massive advertising budgets

Feed your ADHD brain with premium fuel
Sleep 8 hours a night and stop listening to people telling you to “sleep less so you can do more”. You’ll outlive them.
If you are unwell, have blood work done, identify nutrient deficiencies, and supplement to fix them. Most people are operating way below their true capability.
Meditate daily to reduce the noise and confusion.

Spend at least 20 minutes outside in the sun for fresh vitamin D. Maybe incorporate your exercise at the same time.

Note that all of the above are relatively low cost, if not free. If you do nothing but these few things on a weekly basis, I promise your life will change.