Which if youve done flips , but not commerical multi before, you wont miss much,  however a 6 fam is a commerical code permit so there are slight variations between the residential code for essentially all trades which if you dont have a detailed plan and you dont double check every code before you do anything but rely on cheap labor to do your due diliegence for you, what could go wrong ? 

There are many variations of HUD programs including Section 8 (disability, veterans, etc). 

Do not nickel and dime tax variations.

@Joe Cassandra History repeat itself but we should understand that recency bias often make us think that the exact same results will happen but expect variation.

There's a tremendous amount of variation just on minor differences.   

@Clayton Barnes thanks for the heads up on the variation within the loop.  

Another variation that could be an opportunity to increase your rent would be to lease your townhome to someone like him to do AirBnB arbitrage - basically, he leases it from you and you let him sublet the unit for STR stays.

You do know there's great variation of quality and thickness in these products?

I agree with Greg—there are many different variations that exist with slightly differing formulas, modeling, and assumptions.

The variation IM familiar with is " Live where you want to live, invest where it makes senses."