Does a property with an owner-occupied unit have differing "ideal" numbers from a pure investment property?
Purchased a duplex last year, moved into it from our SFH. The idea was to get us into a neighborhood we wanted to be in, and to do so without the burden of ridiculous property taxes. (The taxes on my 150K Duplex are now $4300/yr. They were $4800/yr before I appealed the assessment.) Many SFH in the area go for more, and have taxes of $4-5K/yr. I couldn't stomach the thought of paying $400/mo just for TAXES even when the house is paid off!)
So, we just made sure that if we changed our minds down the road and wanted to live elsewhere, that whatever we bought would cashflow something more than zero if we rented out both units. Because I'm not doing it soley to make money on the property, I was looking for the RIGHT property that fit our criteria. (We literally did have a list of requirments we felt were necessary.) I didn't want to add the unnecessary burden that the property also be an awesome deal if it was JUST an investment, just that it made something if needed. But I plan on staying here a while, so the main thought is that this is my HOME. So what I was really comparing was my out of pocket monthly cost to that of a single family, and then deciding if the difference was worth the hassle of a tenant, maintenance, sharing space, etc.
So, for us, we bought a duplex for 150K. Need 20% down for that these days unless you do FHA. So 120K mortgage, and add in our huge property taxes, and total payment with insurance is $970/mo, + $40/mo that I pay for the tenant's water/sewer/trash pickup. But, I get $800/mo in rent from the other unit, and we share internet. So my effective monthly cost (Obviously maintenance costs change this) is $210/mo. A comparable SFH )(Same living space) would be $130-150K in this area, and thus would cost me about $900-1000/mo. Even with maintenance, upgrades and vacancy, I expect in the long run the duplex will be worth it to us.
Again, I'm dismissing the tax benefits of the rental income, the maintenance costs that I will incur on the other unit, etc. But the point is, I think how you look at the numbers depends on your motivation for buying a multi-family, and your plans for it long term.