Not much to add about the nuts and bolts of how to do it, but your question of changing priorities resonated with me. I have an answer but it will take some work. First, I have to admit a professional bias...I am a shrink...but I really, truly believe that in order to make a commitment to taking better care of yourself, you have to believe that you are worth being a priority. Now I am not saying that you are a head case or anything, but most women have self-esteem issues in some form or fashion and are used to giving, giving, giving to others, often at the expense of ourselves. Changing to a healthy lifestyle will take time and effort, and if you don't believe (consciously or unconsciously) that you're worth that, it won't happen. So my advice would be to try to journal your feelings in that regard, maybe check some related books out of the library, or if it really hits you hard, see a counselor and explore it a little bit. I think doing it for your (future) kids is great motivation, but they're not here yet and you are, and you deserve the best you can get all on your own.
This has me thinking of one of my favorite quotes: "What you feed grows; what you starve dies." Feed your good habits and your commitment to yourself, and try not to give the negative excuses a chance to get any bigger. Good luck!
And now that you don't have to be perfect, you can be good.