I have the same query about the sentence which has already been highlighted, suspect I just don't understand your thinking there.
Apart from that, I think it is a powerful re-introduction to bdsm activities. My only other observation is that if I was your sub, it would work most effectively if I was given a period of time, maybe a week, to carefully think out what I was going to offer in my letter. That would not only provide a build of anticipation on both parties, but would give her the opportunity to really think through the options, meaning she would be more likely to include everything she wished to, and not include things she did not really wish to.
Hope you both enjoy...
cariad