I always highball my numbers. For example, if it is a sfhI will throw a 100 at capex and 100 at repairs per month even though on the rent it might only be 900 a month, and if it can cash flow even with really high numbers then it might be worth trying to find more accurate numbers. But for each area repairs and capex are a different amount, for example, I live in great lakes so there is a lot of snow and moisture. So I would have to take those into account on top of a new roof or a broken toilet here and there.
For vacancy, you can usually look up the vacancy rate for your area or talk to other local investors to find the vacancy rate I know for my area after talking to multiple investors its about 6-9% but that is only because the rents are really high for the area due to property taxes. The best advice I can give is talk to the locals, even just homeowners they don't have to be investors. good luck and fair winds!
