It is a very thorough letter, but I wonder if it isn't a bit too thorough? You mention it is for family people who don't know but didn't say who exactly. Mother, father and siblings or long distant cousins? Sure the folks need to know stuff, but I don't think I told mine anywhere near half as much... admittedly I told mine face to face and burst into tears but I still think I managed to tell them everything they needed to know. My brother who I'm not that close with is going to get a one paragraph email. Cousins, who I never see anyway, aren't getting anything.
The level of detail is up to you of course, maybe your folks are the kind who need every fact to be convinced... I thought mine were too but apparently not.