I understand the desire to write a DA letter and how theraputic it would be but to me it says,
A )You view them as someone with actual authority. In your letter you stated in so many words that you don't believe they represent God nor do they have the truth so why do you feel it necessary to explain anything to them especially anything as personal as your relationship with God.
B) You care what they think. You've explained that they are spreaders of untruths and that you have received more love from non JW's than from those in the Congregation so why bother with them? Most of the time in life we just walk away from or distance ourselves from people we don't trust or those who seem like they don't care about us. To announe it to them beforehand seems childish and needy....even sort of "drama" based. "You're not nice so I'm never going to speak to you again"
C)You want or expect them to take the next step in the process which is Disfellowshiping you. When you write a letter like this you are drawing a line in the sand for them to step over. As legalistic as they are, they will have no problem exercising their "in house" self appointed authority. You've made it easy for them. They don't have to do any homework or gather any facts to find out what is going on with you. You've spelled it all out for them and you've put it all in writing, nice and legal like for them to file away for anyone to dredge up in the future.
As much as you'd like to give them a piece of your mind, what you're really doing is burning bridges behind you. You sound pretty young and it's easy to be impetuous when one is young. You are giving them the power to yet again have some sort of say in your life and to have an impact on it forever. There is no where in the Bible that says that you must write a letter to anyone explaining your beliefs and your actions. This is their little custom. If you don't acknowledge it....it doesn't exist.
Have a little mystery about yourself....let them wonder about you...give them nothing.