I had also toyed with a similar idea. Displaying a set number of words from your article body would not be the best idea as you are restricting yourself somewhat to always providing a good enough "abstract" in that amount of words.
Your first idea of using fckeditor within your AddEditArticle.aspx is certainly the better of the two and as it is quite easy to see from the body field how to implement this for the abstract. Also you can create a custom toolbar set within FCKeditor to limit the number of formatting options within the abstract (perhaps you ONLY want to allow for images to be added and no other formatting).
My problem with this approach, and it may not be an issue for your site, is that if your aim is to display just one image within the abstract, it could be quite difficult to ensure that all abstracts are formatted in the same way.
Personally, the way I would achieve this is to create an Article ImageUrl field (similar to that of the Categories) and then use an asp:image control on your article listing, and bind the ImageUrl to this. As with the Categories it would help to keep your article images the same size to preserve consistent formatting.
Whilst this solution may actually be a bigger task than plonking another FCKeditor control on your AddEditArticle.aspx page, it would certainly be the most logical in my eyes.
Hope that helps.