Much of Oakland Township budget, investment and audit reports can be accessed from the Township Treasurer website here:
A chart from that website provides a very good summary.
Here is a chapter on Board of Trustee responsibilities from a MTA guidebook condensed into bullet points with references to state laws.
See audited financial reports for any Michigan municipality plus organizations like libraries at this site:
Oakland Township Budget Reports
Budget reports are the best way to examine what the Township spends money on and where the money comes from (not all is from your real estate taxes).
See recent (back to 2013) budget reports on the Township website here:
Here is an older report (no longer on Township website) going back to FY 2006-07