Bonus Tip: If this quadruplex is out of state, I’d highly recommend building a reliable local team (cleaners, handymen, etc.) and maybe consider hiring a co-host or VA to help with day-to-day tasks, especially if you scale up. 

It's also easier to handle dips in census similarly to dealing with rental vacancy if you have one rental property compared to a larger apartment building.My wife loves the operations but we have steadily been working her out of the day-to-day stuff. 

@Polat CaglayanI've never seen a formula but here is a general rule of thumb for multifamily:The class of an apartment refers to the quality of the building, which can be determined by a number of factors, including age, location, and condition: Class A: These are the highest quality apartments, typically built within the last 15 years.

Back yard landscaping is usually the biggest expense at $5-6k for artificial turf and rock, but doing this sets you apart from the others.

However, with high rates, the next mortgage would be very expensive, and a vacancy would be intensely expensive with two mortgages.

This normally would not be an issue but the cost of the water/sewer is extremely high in this area and specifically because the meter is a one inch, the costs are much higher than a normal 3/4 inch on a non-duplex. 

I sold an apartment building and as I lived in the building was always there when my realtor showed it to prospective buyers. 

high interest rates have hurt cash flow and long term rentals are still a great investment... they're just not going to throw off rental income in the first few years of ownership.

I highly recommend you start going to meetups.  

So when you hire that able handyman and give him keys to all of the apartments and the security codes without learning that he is 90 days out of prison for breaking and entering and committing assault and kidnapping your umbrella coverage may not help.And, these days, a million dollars of coverage will deal with the contents of a small truck that you sideswipe and it bounces around a little with the electronics inside.