Project list with indentations and the possibility to create/display list of the linked activities

screen of project's creation

Which screen do you mean ? Project Screen ?

to be able to represent projects list

Where ? In the project list or project screen ? In select list boxes ?

- with the identations

As alread explained, it will not be possible in the main Project List as this list can easily bze sorted by anything else but wbs.
For instance, clicking on name column header sort is applied without possibility ot change content, so indentation will be a real mess.

with the possibility to expand or collapse some part in function of projetc or subproject

Will technically no be possible in the main project screen list.
No, really, no.

But you just have to use the planning portfolio view : through this view you can create projects with exactly what you want.

- with the possibility to create directly and display the list of the linked activities (with the progress bar)

This is subject of request #1988

- with the possibility to assign directly the activities to the team

How do you expect to do this ?