You can certainly borrow money from your 401(k) in this fashion....if your 401(k) would allow it (your plan administrator or the plan "terms and conditions" would be able to tell you). 

I've looked at creative lending options but none appear to work other than old fashioned saving and a conventional loan.

ADR and Occupancy rates are more of an art than a science, but using sites like AirDNA are great places to start and then verify thru local property management or just good old fashioned research on Airbnb and VRBO for active rentals in the area.  

Might have to do this the old fashion way... sorry :-)

You are the future investor, you are the future real estate agent, or whatever it is you want to be, it is so important that you are guided in a considerate fashion, and taken seriously about the goals and actions you are capable of pursuing. 

Everything else has to be refreshed : Floors (carpeted, heavily spoiled and cat urine odor) Ceilings dry-wallWalls dry-wallElectrical is out of date (knot and tube all over, electrical panel needs replacement) Risks: Sanitization (cat urine smell, potential for pest problems)Structural integrity not checked (unable to check in a timely fashion due to deadline)Evidence of water damage on main floor ceiling, extent of damages unknownNo smell of mold in basement but knowing the city history of flooding, this is uncertainPlumbing looks recent but it was hard to be absolutely sure of this assertionThe reason I decided against in the end : too many unknowns.

I truly believe in real estate the old fashioned way, and believe it can still be done. 

I thought Forbes did a nice job on this article over the weekend and wanted to share it here on Bigger Pockets because it seems to capture some big ideas that may take a lot of digging to find otherwise and lays them out in bullet point fashion.  

We're old fashioned, so please don't suggest cryptocurrencies! 

You also may have a claim if the addition is pulling away from the home in a reasonably visible fashion.