Dear Sly Apple Pie,
If you are still interested in getting feedback, my opinion is: don't send this letter to her.
There is passion and love behind this letter, and that is good, but it seems to me that letters "baring one's soul" and putting everything out there are usually written for the benefit of the sender rather than the recipient.
The love, passion and desire behind a letter like this may be absolutely sincere and incredibly powerful, but the subtext of such letters tends to emphasize the writer's desire to express himself rather than the love that he is trying to express -- it can come across (unintentionally) more as focused on stabilizing the writer's emotional equilibrium than on communicating love to the recipient.
And, yes, most women I know would be freaked out by this unless it were sent by: 1. a boyfriend, or 2. someone she was already in love with.
I know that doesn't mean every woman would react this way, but it's helpful to keep in mind.
If you are determined to send it, my advice would be to trim it down a bit (as another poster wrote: K.I.S.S.), remove anything that may express indecision or lack of confidence, and focus on the emotions and the heart energy --- expressing yours sincerely and directly, and synchronizing with or awakening hers sincerely and directly. Really put yourself in her place and imagine receiving a letter like this --- how would she (not YOU, HER) feel? How would she react? What would feel too aggressive? What would resonate with similar feelings of love within her?
One more thing: you can give her a traditional gift in addition to a letter. I would recommend it; the letter is for YOU to express your love to her, the gift is for HER to receive unconditionally.
I hope you don't interpret what I've written as criticism; I don't mean it that way. It is obvious that you are sincere and passionate and have deep feelings for this woman --- just be sure that whatever you do is helping your relationship rather than hindering it.
Whatever you choose, I wish you the best of luck in your relationship with her!