It depends on the data source and the size of the transnational data of the domain. And how many years you capture for the dashboard and the size of QVD and QVW varies in that manner.
For normal and good dashboard the sheet numbers would be 5-6 sheets but it depends on the scenario and this numbers are vary from reporting requirement. And for the QVW size may be max that would be <= 500mb approx also the QVD that store compressed data and data reading from QVD is faster in compare to another resource then that may be also vary from domain to domain.
