replying in order:
1. missing ini files - that's weird. I don't get that on my test system. Those translation files are for the system and authentication plugins. If you open the plugins and see things like PLG_SYSTEM_EMAIL_BLABLABLA - then there is a problem. Otherwise, it's joomla being weird.
2. I don't have anything that I've published, however, I've created something like that for one of my sites. It doesn't edit their username, it assigns one and hides it from them. The idea is that they always and only log in via email address. The usernames it creates are something like user12345 (where 12345 is the user id). I'll look at that and decide if it's something I want to release.
3. The types of authentication you allow on your site depends on which authentication plugins you leave enabled. If you enable "Authentication - Email" (my plugin), then you can log in with email address instead of user name. If you leave "Authentication - Joomla" enabled, then you can log in with usernames. If you don't want usernames, disable "Authentication - Joomla"
