i have a few clients that have apartment buildings, the most successful ones (and least stressed) say ALWAYS buy something 12 units or bigger, then you can give someone free rent to be an apartment manager. and the taxes/insurance/maintenance/etc are almost always less per unit on a bigger deal.
if you don't have someone onsite, you are going to be taking phone calls about leaky faucets and broken toilets all hours of the day and night.