Exactly ! It is a bit hard at first to snap the both midpoints intersect in the middle but the you'll get used to it. And regarding your guidelines, you just need to select the face before picking the rotate tool and then you can rotate the face without worrying about rotating the guidelines. Well.. you said it first !

Depending on what files you have installed you might also find Thomthom's tools listed under a sub-menu in the Plugins menu ? Solid Inspector needs a preselected group or component instance to 'inspect'...