BuddyPress.org

Currently I am setting up BuddyPress for a discussion board with more social features. Therefore I want to have a display name only, because a real name wouldn’t be used.

I know that there is an old plugin “BuddyPress Usernames Only”. But I want nick names with accents (especially the german ones). And here someone says that UTF-8 in user names could be risky, e.g. for SQL injection:
http://bbpress.org/forums/topic/accents-in-username/#post-67473

So my thought is:
1. There is only the Display Name on the registration page.
2. The “user_nicename” is automatically created from “display_name” (instead of “user_login”).
3. In the front end every “user_login” should be replaced by the “display_name”.

A note for step 2: It would be best if (german) accents would be converted correct: ä=ae, ö=oe, ü=ue, ß=ss). And “user_login” can be the same as “user_nicename”, because it wouldn’t be visible any more. For login there are Plugins to use the email address instead of “user_login”.

At this time I am not familiar with the plugin system to change functions without changing the core. But I am willing to make step 3 for my own, when you can give me one example (or is it possible to change it for the whole front end with only one change?).