Quality of the tenants2.

If you hate the process of placing tenants, it may be worth it to hire a property manager to handle tenant placement for you.I think finding a new tenant is a better long term strategy if you're confident you can find a higher quality tenant that will cause you fewer headaches.

If you're willing and able, I do recommend the "house hacking" strategy which is just a fancy name for buying a rental property and living in one of the units, because you'll get very favorable financing - an owner-occupied fixed-rate 30-year mortgage.I'd also say, analyze that property as if you won't live there and it's a pure rental, and make sure the property is still cash flow positive if there's a tenant in your unit because then you'll know if it's actually a good investment.And when you analyze it, include payment of a property manager in your #s because if you don't, and doing so would make it go cash flow negative, then you've just bought yourself a job because you literally can't step away from managing it without losing money.

For example, should we focus on acquiring one high-quality property in a strong market, or would it make more sense to spread the investment across multiple lower-cost units in emerging areas?

So as @Melanie P. said, any positive cash flow is enough. 

@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.

Are their listings detailed with good quality photos?

But if your goal is to cashflow positive from the Day 1, you may find it very challenging due to current day interest rates, high cost of construction and the fact you won't have the efficiencies of a seasoned developer building at scale.

-------------------------------------------------------------------------------------------------------Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

Thanks to COVID, for a couple of years, you can actually make enough money to be cash flow positive even if you hire a property manager AND have mortgage payments.