So, as suggested, `max-width` is much better as it allows smaller screens to "squeeze" the page together, while it will simple "max-out" at the defined size on larger resolutions.
Having done some development over the time myself, I find [markdown](http://daringfireball.net/projects/markdown/) really easy to learn (and learn). On top of that, it's also widely used. So user's don't have to re-learn a new syntax. Additionally, I would say, stay away from JavaScript WYSIWYG editors. From my experience, they are not yet that usable. I have to say though, they have been enormously improving over the last ten years. And maybe there is one that's working better than what I am used to. But given that the allowed set of markup will most likely be small, there is not a lot which speaks in favor of WYSIWYG editors.