This is such a great question. You've already received some great advice on the blog logistics end, from the prior answers, so I thought I might take a different approach... how do you start generating your content? My advice is...
First, be generous with yourself. Be kind with yourself. Being vulnerable is the strongest, most brave look we can flaunt, honestly. Especially when talking about our struggles.
As you sit to write (or visually share) your story, there are some great tricks to rev your engine: Write your blog like it's a letter: to a friend or loved one, to an imaginary soul, a spirit, to you in the past or you in the future--whoever brings an energy to you that allows you to be open and expansive and kind to yourself--write your post to them. You can even delete the "Dear So & So" bits once your done. Sometimes, when we write in a formal setting or for a public audience, we go stiff. Writing to a loved one can break that open, and then we just delete the evidence later, if we feel like it.
Also, don't forget that you can include pictures. These can go beautifully with words--maybe you will meditate on an image and write a few lines on that, and then jump to another. This creates a visually engaging blog and another way to keep generating content.
Other prompts: What do you wish someone had told you? What unintentionally harmful statements do (unknowing) people say to those managing an eating disorder? What can you tell us all to be more thoughtful about? And how can that show someone who is dealing with an eating disorder, a little kindness and connection?
If you don't like carrying pen and paper, use the note function on your phone--make a folder called "blog" and whenever you have a fragment of a thought--a beautiful sentence, a topic idea, put it there. You can open it later when you are ready to sit down and work. This way, inspiration can strike whenever, but work time will always be front-loaded with notes to build off.
Good luck! This sounds like a great project.