The jfbcjsactivity plugin is meant for pushing status updates that users make in JomSocial to their Facebook Wall. If you don't have JomSocial, don't install it.
The JFBCLogin module is no longer a part of JFBConnect. In it's place is the SCLogin module. It works for both JFBConnect and JLinked, and it's recommended you move to that. It was installed with JFBConnect 4.1.x, just like JFBCLogin was previously installed.
The version number for the SCLogin module is a little wonky right now, since JLinked is v1.0, and that's where the SCLogin module was first released. We're considering up-revving it so it's more consistent. However, the most recent version of SCLogin is 1.something (can't remember) and it has all the features of the JFBCLogin module, and a few more. You should use it
Hope that explains everything you were looking for!
Alex