I agree with Karin that shorter is better. Perhaps three would be a good limit. Short and sweet. However, the number of articles would depend on how long they are.
One suggestion I have (if possible in your e-mail), would be to include images with your articles or events. People are drawn to pictures and may be more likely to read the content.
Hope this helps.
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.