1. This is not possible.  While reading permissions can be seperated from posting permissions two ways, there is no way to limit this to a simple comment type function.  This would mean you would have to alter two pages minimum to allow this plus some additional logic.  Currently, this is not a roadmapped thing and I don't see any reason it will be soon, if ever.

2. The button being inside of the editor itself, as another button on the editor, is actually handled in your html provider.  This is not isolated to the forum module alone.  You would have to change your provider to change this, and it would affect all users.  Now, I am not sure about FTB but with other editors like Telerik I can use a single provider which has rules to show some buttons to some users and additional buttons to admin type roles.  Regardless, this all comes back to your html provider implementation.