1) If several activities (connected by a "parent") => Request (like copying) to remove the entire structure

Some cascade deletion ? Maybe dangerous. To be studied. Recorded as Ticket #960.

2) Same for a project (activities, milestone, structure ...)

Included in Ticket #960.

3) Change the combo box "project" views activities, project milestone, ... that which manages the project (top left). Objective: To limit the list of proposed projects

I don't understant the request. Could you please explain ?

4) When you created a ticket is necessary to save before you can add an attachment, in the future it may be more efficient to be able to upload attachments before saving

Should reconsider the complete design of saving. Not easy. Maube for V5. Ticket #961 recorded.

5) Via assignment, you can assign the same person twice on the same task. This can cause to errors ...

It is designed like this and may be usefull. Personnaly I use it to keep trace of initial assignment. It task need extra wrok, then I ass new assignment instead of changing existing one. So I keep trace of original.

6) When changing an activity structure project, the new project is not affected stain girls activity => Inconsistencies on monitoring.

I don't understand. Could you explain ?

3) Change the combo box "project" views activities, project milestone, ... that which manages the project (top left). Objective: To limit the list of proposed projects
I don't understant the request. Could you please explain ?

In all objects (Ticket, action, project, risk ...) it selects the project with a combo box that lists all projects in the database including those that do not see the CDP. For me it impacts 2:
  - The selection is more complex (thank you for the improvement of V3.1)
  - A contact (customer) also see the list of all projects managed by the company ....
If we replace the combo box of objects with "Project Combo Box" that filter the list according to rights

6) When changing an activity structure project, the new project is not affected stain girls activity => Inconsistencies on monitoring.

It is not very clear .... sorry
If you change the parent activity of the project, sub-activities are not assigned to the new project

In all objects (Ticket, action, project, risk ...) it selects the project with a combo box that lists all projects in the database including those that do not see the CDP. For me it impacts 2:
- The selection is more complex (thank you for the improvement of V3.1)
- A contact (customer) also see the list of all projects managed by the company ....
If we replace the combo box of objects with "Project Combo Box" that filter the list according to rights

It is already the case.
You can try (I just did it to be sure there was no regression on expected behavior) :
- create user 'test' with profile Project Leader
- Affect 'test' to one project only
- Connect as 'test' : list of projects (in combos) is limited to affected project and its sub-projects.

If you change the parent activity of the project, sub-activities are not assigned to the new project

This also works correctly, as you expect it to.
You can try (I also did it to be sure).
Structure is
Project A
=>Activity 1 (belongs to project A)
=>=>Activity 2 (belongs to project A)
Project B
Move Activity 1 to Project B : Activity 2 is also moved to Project B and new structure is
Project A
Project B
=>Activity 1 (belongs to project B )
=>=>Activity 2 (belongs to project B )