1. At the moment we don’t have builder for category template, but you could use landing page and filter the modules to certain category and this page to menu to replace category menu. For removing category slug you might want to try 3rd party plugin for that, such as: Remove Category URL.
P.S. We never tested that plugin with JNews yet, it may caused issue if its not compatible.
2. Please install JNews – Customize Detail Category & JNews – Extended Category Option plugin to have more option to customize each category settings.