Maybe selling into something with better numbers or lower headaches is the right decision for you, however I want to encourage you to speak with a few different experts along the way so that you can account for all of the important variables. 

Prior to about 15 years ago the PM used to call with a rundown of the applicant’s credit, income and any relevant facts and I would approve or deny.

No income verification.

If you were purchasing this 4 unit as a primary residence you could likely use the rental income on the other 3 units as qualifying income.

The challenging part is finding an investment that has enough spread to account for all of the labor.

Does anyone see any legal or accounting issues with this plan?  

The current loan would have to evaluate your debt to income with the additional debt etc.

Beware of incoming phone calls.

So all of my income goes toward paying down the principle.

You also have to take into account the local / state landlord laws...especially the ones coming down the pike in CA's November ballot --> "Justice for Renters Act" Not sure if it'll effect STR or MTR but as a general rule of thumb, I don't run numbers on best case scenario.