Hi RĂ©mi, Vidalia does not show the randomly generated password because it doesn't know it (the password is generated, used to connect, then cleared from memory). To use another controller like Stem you will need to chose another authentication mechanism. I would suggest cookie auth - it's the easiest to work with.
If I change any of these settings, then I cannot browse anymore, and TB displays "The proxy server is refusing connections".
That's odd. I've certainly attached controllers to TBB before. After changing the authentication mechanism did you restart TBB?
Cheers! -Damian