@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.

Quality pics are by far the number one contributing factor.

With DSCR, credit and down payment are the major factors (plus the property itself of course) so it is very possible since a lot of the properties in the area cashflow pretty well. 

You have to factor in demand and vacancy rates to determine if it will be more profitable, and that’s specific for each market.

Mainly the "self sufficiency test". 

Depending how much of the neighborhood is a hot zone for renting rather buying, and which Property type is performing better than the other (meaning 1bd 1ba 2 floor renting out faster and much more consistently than a 2bd 1ba 1 floor), you can make your choice of those factors as well as other ones that impact your decision for what you wanna do with your investment.

I mainly want to ask if these assumptions are reasonable and if there's anything I haven't considered:(1) multifamily units in NJ close to New York City, ~$1,000,000, 20% down payment, (2) Using the following assumptions: 4% appreciation rate, 6.5% interest rate and 5.0% refinance after 5 years, $10,000 yearly maintenance fee(3) ~$6,000 monthly rental and assume 3% increase yearly with 5% vacancy rate(4) Based on the above, the calculated IRR if selling at the 10th year is ~19% (considering tax benefits) and ~17% (without tax benefits).

ARV is a very important factor here. 600 FICO is minimum. 

Make sure we're accounting for the appreciation, cost of the sale, cost of the purchase and one of my favorite factors, the risk.

Currently renting the main house as a LTR and the ADU as a MTR.