Mohamed,
You are basically working within an area of our product that we need to improve upon. Aggregate fields have been around awhile but they never had included the tasks application - generally it was because project fields already existed that aggregated Task information (work hours, cost and more recently, revenue). Unfortunately since the task application does not appear in agg fields, neither do custom task fields. All of these elements, when pulled together with another application(s) (and its aggregate fields, like Expenses) would most likely need to have a report bring all of the information together in one place.
Some things can be rolled up via views such as "Milestone Value" if you view them from the Task tab assuming the viewer is correctly seeing all projects on their view. But again, you wouldn't see Expense information in the Task Tab.
The improvement would be for our Calculation field to include all aggregates (native and custom) and standard numeric fields and for aggregate fields to display Task custom fields (since the others are accounted for). One thing that would help is offering suggestions direct to our product team if you have a moment.
http://www.daptiv.com/support/product_feedback.asp
I think today your best option for viewing the fields you've mentioned in a single place would have to come from a Crystal or Work Intelligence report.