Hi @SamuelSh3
To your second question first: In WF reporting you can only ever modify attributes of the business object on which the report is based. If it's a task report - you cannot modify project attributes and vice versa.

If the %complete is inadequate try a Milestone View on a project report. You cannot modify the % complete on these if they have subtasks and are set to auto-complete. But the view should give you an adequate sense of project progress AND you can click through to the Milestone tasks or project.