From there factor in mortgage, taxes and any other expenses.

and a myriad of other factors.

What factors am I missing from the assessment described here?

I think finishing a basement is an easy value add (assuming all the other factors make sense, location, ARV, etc. ) However, if you bought the new build at the price of a similar property with a basement already finished... not sure the equity will be there unless the appreciation/inflation ride goes on...

In fact, passive income has generally a better tax treatment than active income.Flip properties are considered the sale of "inventory" so you are a dealer of property. 

(I expect to factor in this cost when running my numbers.) 

It really depends whether or not you want to go to school and other factors.

Not a hundred moving parts involved is one factor.

The ability to make a positive impact in the infrastructure of local neighborhoods and economies continues to win investors.FAVORABLE LEVERAGE/DEBTMultifamily benefits from the most favorable financing treatment of all real estate asset classes, oftentimes receiving the most competitive interest rates and longest amortization periods.This favorable environment is led by agency lenders, which were originally created to support housing stock.

And there is no real shortage of housing when you factor in migration and desire, in fact many states have a surplus of housing.