Hello everybody,
Nice topic.
1) There is not the choice on SEBLOD 2.0 (there is this feature on SEBLOD 1.x) to display a field or not on edition view. The way today is :
* ("easy) create a joomla user group called "only public", yes you can with Joomla 1.7 create a user group only for guest people (public only, create the access level too, see Joomla User Manager option and the parameter "Guest User Group"), like this you can with SEBLOD assign to a field the good access level. Example, for a captcha field, assign it to public only access means this field will be display only on registration

. So if you wish to display the username field in the registration form but not in edition form, create 2 username fields with exactly the same storage configuration, assign one to public only (registration view) and the other to registered access (edition view).
* to do a custom template:
www.seblod.com/support/documentation/seblod-2x/templates.html
In few time, there will be some Style Form plugin which allow you (like the typo plugin on content) to manage the display of a field input. So it will be easy to do a style form plugin ti display or not a field on edition view.
2) @Wedal, it's a solution, yes. An other one is to not display the Joomla article title (see Joomla options) and to display the field you want in your intro view.
3) You can change the default access of Joomla user article like Wedal describe it.
4) Not sure to understand, but if the purpose is to search only about the user id, put the user id field in search form and in live value select "profil" and put in value id.
Best Regards