1. CB login is in a vertical menu. If I enter a wrong id - password, the CB login forms are presented in the vertical menu and on the page in the site.
That's normal. The login module just does a POST to the login page. You'll see this exact behavior if you're using Joomlas login module as well. CBs login page will use the parameters of the first login module it finds. So if you create a new module to replace the one you currently have then change your previous module to have different parameters then the login page will use that modules parameters.
How can I prevent it (so only in the vertical menu like initial) ?
You don't.
2. Where can I customize the title size of registration, lists, ... ?
Title size? Don't understand the question. You want to change the titles? Registration is a language string in CB language files. Userlists are whatever you supply as the title when editing the userlist. If you're meaning field labels then this needs to be done with CSS; right click and inspect with Chrome or Firebug for Firefox to see its CSS classes and ids.
3. Is it possible to customize the forgot id - password page ? For example include it in an article and linked this article with the CB login links ?
You can link to it any way you like as there is a Joomla menu link for it or you can use the below in a href anywhere you like. You can not include forgot login inside of an article though.
index.php?option=com_comprofiler&task=lostpassword
4. Same question for all messages generated after an action (registration, ...) ?
The successful registration messages are language strings within your CB language files. Please see your CB documentation available for download in the Advanced download section for the location.
krileon
