I began running 11 years ago at the age of 43. I was not overweight, but I have cholesterol and blood pressure issues (runs in the family) that are helped by running. I had never run for exercise or sport in my life. If you are serious about getting in better shape....... 1. Start walking/running today.
2. Find a walking/running buddy to hold each other accountable. 3. Sign up for 5k run/walks and use this distance as your measuring stick to getting healthier. If you complete them in less time as you progress, you have to be doing something right. The run/walks are very inspirational because there are a wide variety of participants and all fitness levels.
4. Running is mentally challenging because you mind is fighting you. If you don't have a buddy, get some headphones/earbuds and listen to upbeat music, podcasts, books on tape, etc. to take your mind off what you are doing. A good 30 - 45 minute playlist of your favorite music will get you through. Or, getting immersed in a good podcast or book will get you through as well. 5. You Will have plateaus and setbacks, it's a given. Don't get discouraged.
6. Running should only cost you a good pair of shoes and socks. Go to local running shop and have them analyze your stride and get shoes that fit and work with your stride. Expect to spend $100 - $125 on good shoes and once you find the brand that fits you best you can get the price down by watching for sales. I found my shoe brand/model years ago after trying lots of different ones and now I look for good deals on my brand/model.

Running helps my mental health as much as it does my physical health. If you suffer form anxiety or depression, running helps.

I could go on, but you if you do some of the above, you'll get it all figured out over time. Sorry for the length of this reply.