Seller decided to back out at the last moment for some arbitrary reason and just didn’t show up to closing to sign the docs.

Lastly, check any shared doors or gaps and add door sweeps or weatherstripping to block sound from traveling between the units. 

You seem to already have US based accounts, so you are good there too.The last item here is the definition of "good".  

Definitely going to consider everything including your last point about 0% interest credit to actually execute the flip and get materials/labor.

Quote from @Zack Marshall: Quote from @Tyler Tyson: I had a very poor experience with them last year.

Assuming you don't have a mortgage that requires a certain level of insurance, you can get a stop-loss policy covering all the properties. 

🎯 Leverage PowerWhen's the last time your broker let you buy $500,000 worth of stocks with $100,000 down?

Out of the four properties , there is one solid tenant, the other is struggling and the last two  properties are not renting.

In some cases, it may not be possible to purchase and store materials, but if it is, that is one way to protect your budget and avoid a costly mistake.The last thing I would offer for you to think about is having a pivot plan. 

You are taking a chance with every tenant and you hope they are not trashing your house and you don't have an eviction.If your condo did not appreciate it over the last 6 (unicorn!!)