(Especially a 2-4 unit.)Do they have friends/relatives/co-workers that would rent rooms from them if they bought a property to show more income?

Just get on Airbnb and see who are the property managers doing most of the units in the area and search for them on google. 

Also make sure you are comfortable with some holding costs if the units don't get rented right away (if vacant).Also look into if there is rent control in the area that the property is located.

Start by leveraging what you already have—consider tapping into equity through a HELOC, house hacking again with an FHA loan, or increasing cash flow by converting a unit to a short-term rental.

Fannie Mae has a requirement that if you want to use the rental income from the non occupied units, that you MUST have a current housing expense which means you cannot live rent free.

.- **House Hacking:** This can be a great way to start, especially if you're looking to live in one of the units.

And then I want to progress into single family units and so on.

I recommend starting with turnkey multifamily 2-4 units if you're a beginner.

Let me know if I can be of assistance. 

i do not however use it for heat mine is an AC only unit I believe not a heat pump unit.If you're whole unit is relying on one mini split for ac and heat that surprises me just given if you shut a bedroom door you'd not have heat from the split that I assume is in the living room.