For installing the plugin, you should first remove the two files you copied there. Then, use the Joomla installer to install the plugin (in it's tar'd format) from the /admin/packages folder. That will properly add it to Joomla. Copying it doesn't work.
Not sure why you run into that issue in the first place though, but it's possible it's because those files already existed.. but it wasn't installed properly before.
As for copying your configuration, we don't have a good way to do that, and copy/pasting from the database wouldn't work as there are multiple unique values per site that need to be different for each site. It's a good idea to have a way to 'merge' site settings, but just don't have any way to do that now.
Good luck,
Alex