Questions of Analysis and All Things NOI

Just looking for feedback from anyone who would like to share. As my wife and I research and shop for our second real-estate investment, I find myself overwhelmed with questions in regards of what assumptions to use. We have one single family investment, and we seek to purchase a multifamily duplex investment. In general, my analysis seeks a minimum 5 percent cap rate, utilizing 10 percent for vacancy losses, and 8 percent for each management, repairs, and capital expenditures. Anyone have any input? When to adjust these numbers up/down? Just looking for a little help.