Answer for first question:
To move your Q2A site to other directory. You can copy and paste and since you are using the same server and database you do not need to change anythign in qa-config.php file. That shuld work as it is.
However you need to modify site url from database that you can find in qa_options table. Also you need to udpate your site url whenver you define either in any plugin option or hardcoded.
If you don't want to touch database than you can use a trick. prepare everything on your current site and than from admin section change yoru site url to new url ( make sure once you save this option site may no longer available till you move to new path ) If you have other palces where you need to set path apart from core qa site url than do that first before you change it from admin site url setting.
Answer for second question:
Currently no rating option or repository for Q2A plugins but most of the plguin works fine as far as I know. Curretnly each plugin deliver different functionality so there is not need to compare for review. If you are talking about the quality than there is not rating, review or feedback available on Question2Answer website yet ( hope in future ). However none of plugin is harmful as I know. I may wrong in some cases.
WordPress earned millions of user and thousands of develoers if not millions. In that case you may have options for more than one plugin delivering the same functionality and there you need to knwo which plugin is the best in terms of reliability and functionality. But the current situation with Q2A is different where most of the plugins are delivering unique functionality from eachother.
But personaly I also would love to have Question2Answer's own repositroy where all developer can place them plugin and community can grab from one place instead of individual site or github accounts and that's how only possible to get feedback from the plugin users as well as that can helps to track bugs etc..