If you understand the principles behind website templates you will immediately see the huge benefits to WordPress template systems. Basically it is designed to hookup automated template ideas to a system via which a client who knows nothing about anything can access your site (behind password protection obviously) and update and manage the website that you leave him.
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.