I can't provide legal advice or assist with your closing without having you retain me, but happy to answer any general questions here. 

The house was built in 1932 with plaster walls and ceilings.

@Drew Slew My opinion, you might want to take a look ROI e.g. if you are paying off some loan with 20K and that loan is 6% in interest , try to search if you can invest that 20K somewhere that can yield 12 to 20% ROI so you can just think of it that have 6 to 12% positive and just retaining the loan.

You might be able to give her 10% more per month until done, Remind her that if she starts eviction you will have to retain consul and even if she's successful she's likely to lose more then a months rent.

When your back is up against the wall, you tend to become more creative than you could have ever imagined.I've made a lot of new friends along the way.

On the other hand, if there other units above yours, consider whether their windows are allowing water into the walls even if yours are sealed well on the outside.

Why not install either a mini-split or a wall furnace in the smaller unit?  

Hopefully you analyze the neighborhood that you are looking to purchase inHowever all of the things you stated are important but when it comes to inside the four walls bedrooms should be at the top of your list then bathroom and square footage also.

I'm looking into purchasing a single family home, The platform is perfect to add a few kitchens and walls and turn it into a duplex or even a triplex.

New HVAC/ducting, drywall, windows, walls removed, etc.