I'm not sure what you mean by different automatic actions. The main one I'd think you'd want is just news.reads for all of them, but if I'm missing another auto-action you'd want, let me know.
As for the Objects and categories, please note that JFBConnect understands the nested category and will choose the closest object that matches the current category. So, if you have an Object for the top-level category in K2 which encompasses all sub-categories and then another Object for just 1 sub-category, the 2nd one will be used always for that category. You'd need to associate any actions with that sub-category object that you'd want it to take advantage of.
That gives the most flexibility over how actions and objects are configured and triggered.
Alex