The Details are important _ Pay special attention to the details. They affect your readers very much. Details like alignment of the texts and the number of lines which your paragraphs include, can make readers bored or can interest them. Try not to make your paragraphs longer than 3 or 4 lines. When your paragraphs are short, people will read them easily. But if they are long, it will seem overwhelming to people. The colors you use in your newsletter design is important as well. So you should know a little about colors psychology. It's not hard. You must already know about the effect of every color on people, before designing or choosing your newsletter template.
Buy business web template with total customization option. You may get layouts in the market designed superbly but with little scope of customization. On the other hand if you go for open source developments like the Drupal, Joomla or others then you should buy layouts designed for particular themes. Otherwise your developers or the designers will face problem to make layouts completely fit for your business. Even in SEO related changes there will be problem.