Would I be shooting myself in the foot by using a div with attribute contentEditable="true"
as a text field rather than a textarea?
It would work fine, but it'd be a little bit more difficult than a form, simply because you're going to have to wire up your own logic to make the button's click event track down the correct div, get its content, and then perform the submission. The advantage of a textarea is that the browser takes care of all that for you.