I just want to encourage you on this goal! It's a great goal to have, and I think you can do it. A year ago I wasn't able to walk 5k, either. No way. But I had moved to a new neighborhood and it was really beautiful, so I decided that I wanted to walk around a bit each night. I went to a local running store to get some good walking shoes, and when I found a great pair, the woman who helped me said, "If you ever decide to run, these are great for running, too." It kind of made me mad. I said, "No. No running. Only walking. Thanks." :) After several weeks of walking a couple blocks each night, I decided to see how far I could run, just as an experiment (about a block, by the way), and it just grew from there. I did a 5k race with my brother about 5 months later, and now I'm up to 4+ miles and I really love it. There are some great programs out there (you can google "couch to 5k") and tons of support. I wish you lots of success! You can do it! 

 One other note of encouragement - I think your list of the 3 things you need to accomplish your goal is perfect. But also, don't feel like you have to wait until you have the perfect diet or are in great shape to start. I started when I was eating a terrible (terrible) diet and was in very poor shape. But after I got going, the desire to improve had a very positive effect on both those things. Good luck :)