Thankfully, Northern VA area has robust rental market, so I would rather buy something that doesn't have an existing tenant and then put a brand new tenant, and that way have full control. 

By safely retire I mean <1% chance to have to do anything besides manage your property manager.Many guidelines exist for retiring with a portfolio of stocks and bonds, from safe withdrawal rates based on simulations, to specific bonds/stocks mixes at every age.  

I honestly didn't know they exist: the broker who rent the house out for you!!!

But for all intents and purposes, the best way to go about it is to secure a contract with him to buy his house subject to the existing mortgage, which will absolutely get the trustee to call off the auction, then refinance it out in your name.

The existing structure itself matters.

There is the possibility of finding a distress, condo in south San Jose for about 100k condo apartment conversion, it's just a very competitive market probably won't find on MLS does deals but they exist.

Never select any applicant that you know will be a bad fit out of fear.Choose the tenant that is best for you and your existing tenant. 

Its driving up existing home and ranch values in those areas. 

So, you can foreclose on him if he doesn't pay you and you would do that subject to the existing senior lien, which you would have to pay off eventually.Be careful if you become a lien holder and subsequently try to foreclose.

The banks would factor in the pre existing income from the remaining 3 tenants into the size of the loan you would have to carry in order to take ownership of this 4 plex.