Just my total personal view.
I resigned. I always recommend not using their loaded bullshit language. I didn't disassociate from my friends. I left a cult. It's not my fault that my friends and family still in are brainwashed from associating with me. Thus, I resigned.
Keep it to one side of one piece of paper. Be concise. Think bullet points. They get Russian novel sized letters like this every week. They sort of scan them. They'll always read concise ones.
....Unless you need to vent for you. Just realize that if it starts heading into page 3, you're writing more for your mental sanity than for the statement it will create at HQ. Trust me, the ones they trust to read these letters are numb to them. What they're looking for more than anything are clues as to other apostates whom either 'infected' your or whom you might have 'infected'. (apologies for the harsh terms, that's how they view this stuff. They're cruel)
The bottom line question is, what do you hope to accomplish with your letter?