I would keep it as short as possible and rather send two shorter emails than one long one. Personally, I want to see the thing that is relevant for me in the first paragraph. With so many emails in my inbox, I only scan in the first round and take a second look only if something caught my eye.
You can say in your first paragraph that you will cover 1), 2) and 3). That may get me to read all of it as well.
Other people may have a different approach, though. This is only my preference.