Change Defaults/Titles, Group Invitations

I have a few questions/issues:

I would like to change some of the titles of member groups, for example: I would like "fans", as in members of a group, to be called something else, and "friends" to be called something else. Where would I go to change these options, to take effect everywhere on the site?

Also, on the main Groups page, "Recent Public Groups" is displayed. Is there a way to change this as well, to display recent groups that are viewable only by members? To a guest, it doesn't matter if it just says "private".

Is there a way to make the default country choice in the dropdown United States?

Lastly: when I invite a user to a group, the user successfully receives an e-mail notification, however, nothing happens on the site. Any idea?

Thanks!

I figured out how to change the fans and friends titles in the lang files, but if the other issues could still be addressed, especially the recent groups issue and the group invitations issue, that'd be great, thanks