Hi Sepp.
You can filter reports to specifically report on a given client or project. The HTML report format can also provide aggregated totals for the report.
In order to enable HTML reports, navigate to Setup->Reports->Format and select either 'HTML' or 'HTML and CSV'. Once one of those two are selected, a new option will appear 'Grand Total'. Check it to have the HTML reports include a total.
CSV reports don't include a total, and yes, you would need to massage the data any way you want within Excel or Numbers.
Ernesto.