What is the standard for reposting anothers articles on your own site

Attribution is key. But I don't know enough about FairUse to say what the magic upper limit percentage of quoted material is.

You can generally get to the beef of an article without posting more than half. Also, adding your own commentary makes your site more interesting.

But don't be evil: linkjacking is annoying.

Why repost at all? Isn't this what links are for?

Often a summary or small excerpt is useful for readers, so they can decide whether it's worth following the link.

No more than a paragraph or so, though. It should not take more time to skim the summary/excerpt than to follow the link.

makes sense, so maybe a caption, commentary and the link would be the proper approach