@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.

Taxes, costs, eviction complexity, etc are going to be a much bigger factor in your success than anything else.

Your accountant should be able to factor that into your total cost. 

If you can shorten the window on the cash out refinance to the next purchase/refinance the rate is not really a factor.

Financing is important but your realtor will absolutely be the determining factor whether you purchase correctly or not. 

You can close in an LLC and don't need to provide employment history, income or tax returns, and DTI isn't a factor.

The most popular STR listings in my area have excellent interior design.  

Speed of building a portfolio (Cash-on-Cash return is a factor here)?

What you paid for it and invested in its upkeep are not factors for pricing/selling a property. 

And this low demand could be a couple of factors, either a rural location with low population density or the area incomes are not high enough in order to prevent a rent burdened scenario.