For aggregate and trend data on committees and staffers, see Vital Statistics on Congress on the Best Starting Points tab. For historical listings of members and staffers, see also the KnowWho Directory link on the Members tab and the Database of Congressional Historical Statistics on the Best Starting Points tab.
See also detailed House and Senate reports on expenditures, which includes salaries and spending by committees and Members' offices.
The best source for transcripts of hearings is ProQuest Congressional on the Best Starting Point tab. You can also find hearings text for recent years on Congress.gov and Govinfo.gov.
For congressional documents, I recommend starting with ProQuest Congressional on the Best Starting Points tab.