Amanda Unvarnished

Mmmm pi.

As far as accessibility is concerned, you'll want to test and see which one has accessibility issues you can personally deal with. I'd start with the ones with the smallest feature set.

You don't need that necessarily, but you do need a plugin, since WordPress's classic editor does not support markdown natively. Here's an article that lists several markdown plugins that will work with the classic editor. https://daext.com/blog/the-best-markdown-plugins-for-wordpress/