added a comment - - edited
> How can one prevent an individual URL from being turned into an active link?
I believe the 'problem' is caused by the BBCode filter. The bbcode filter uses regexp to find any text with http[s]:// or starting with www or ftp, and then automatically turns them into links. See the regexp on lines 283 and 289. As a result, it may not be possible to disable this for an individual URL.
> How can I add an e-mail address into a pages text (it's being removed)?
DBOINCP-487, where I propose a fix for this
> How can we make TinyMCE to accept UTF-8 characters (turned into "????" on save)?
This is still an open question, and more research will be needed.