It’s definitely possible to make it work for a duplex or triplex: it really just depends on how much you can purchase the property for vs. the rental economics. In general, the more units in the building the better the economics, simply due to scale. In the Bay Area, it’s generally hard to make the economics work with, say, a duplex. In Southern California, it might be easier but I’m not as familiar with that market.

In terms of how much to budget for renovations, there isn’t a one size fits all rule. The more renovations you need, the cheaper the initial purchase price should be. The higher the purchase price, the more turnkey it should be. What really matters is the all-in cost (purchase price + renovations) compared to the rental economics.

In terms of carrying costs, you can estimate these as a % of purchase price. In California, for example, property taxes are usually around 1-1.5%. You can also estimate maintenance and insurance using reasonable % assumptions.

^ in Bay Area or other competitive market