I think your letter is great and you are full of courage to be able to write/send it.
Just remember--writing/sending was the most important part. Don't set yourself up too high for expectations either way. It may go unnoticed. It may heed unfavorable responses, etc, etc.
Just considering yourself managing that part of your recovery because you've set your boundaries and remember--you can't control their reactions ---all you can do is control your reaction to them.
Hang in there. Be proud of yourself. I did that part, too, and it was so very difficult. I feel your pain.
You just unstuck yourself.......welcome to the 'moving forward' part ---it feels better than anything else in this icky process. I promise.