I'm a sewing teacher and a freelance writer, and I've written several articles that I think would be a good fit for a popular sewing magazine. Their submission guidelines are pretty vague, since they seek articles from their readers, not freelance writers. My question is, since I have about half a dozen articles to propose, should I lead with one article idea, then mention the others briefly at the end of the email? I'm guessing I should start with just one idea and submit the others separately, but if so, how long should I wait in between each proposal?

(The magazine in question is Threads, if that makes a difference. Here's their author guidelines.)

Also, a couple of my articles are rewrites of ones I've published on my sewing website, for the benefit of my students. One was published by an online magazine with a small readership (around 700 subscribers). I made sure to rephrase every sentence and even add some new content, so they're NOT the same articles, but how similar can they be without upsetting the editor? Am I obliged to tell the editor, Hey, this is a rehashed version of something that was published awhile back? I would just skip these articles, but they haven't published anything similar in their magazine and it's information I feel would be beneficial to people who sew.

Any advice will be appreciated.