At some sales they will even accept payment the day of the sale during the auction if that property has not been sold yet. 

However, I don’t yet have the funds for a down payment on another house, and I’m trying to figure out the best option for where to live while I rent the apartment.Do you have any recommendations for managing this transition or tips on finding a temporary place to stay?

With $100,000 cash in hand, the property will be more like in the 400K price point if he were to put 20% down, leaving 20K for closing cost and emergency $.At the current interest rate and RE market is it possible to make 1K after monthly payment? 

Even if you only owe $26,000 on the loan, your payment will still be the same.

The seller would need to include a clause saying what you CAN'T do, which is what a pre-payment penalty would address. 

I offer an online payment portal to submit rent payments via ACH or CC - they "couldn't figure out how to use it" so I set us up to accept Zelle payments.

However you should consider if your loan has a Pre Payment Penalty.

Use the land as down payment on a construction loan.

The current owner listed last years income as $51,000, but currently has rents at (for the five separate units): $650, $750, $800, $825, $1125 (the math doesn't totally add up so maybe he changed a rent payment at some point). 

Hi Pixel, Check out this article about how DSCR loans play into the refinance part of the BRRRR method.