Images, unless they are within templates/tables, should always go in thumbs - they should not stand alone.
I have a fairly hard to explain view of categories - but I firmly believe it should be the universal view. Say there is a Category, Category:Apple Inc., that is part of a larger Category, Category:Information technology. The article that is specifically on Apple Inc, and thus encompasses all of aspects of the Category, should be the ONLY article within that category to be in the super-categories that Category:Apple Inc. is in (i.e. Category:Information technology).
Large blocks of text should usually be split up by sections - no one wants to read what looks like 2 paragraphs with 50 sentences. Wiki sections allow emphasis to be added ''and'' they allow clear organization.