I post several articles a day, some with pictures. Sometimes I use the same picture for a different story. Is there a way to be able to look at the images uploaded for articles and choose among those previously uploaded instead of having to upload again?

'Insert other media' -> insert existing attachment

After adding an attachment to an article how can I add it to article.

There is no "Add to Article" button shown...

There is no default “attachment field” in Pages 4.x anymore. The normal way now is to just use the attachment function of the editor window as you would also do it in the forums.