The husband approached me around July 12th and asked if he could move back into the apartment after she left.

Even when I run the numbers with a 25% down payment, I am having difficulty seeing anything that would even approach a positive cash flow using rough parameters like the 50% rule, except rarely in a class-D "warzone" neighborhood in which I'd be wary to go for a run even in daytime. 

we have made advanced payment for material and other stuff. how should we approach about getting that money back from him?

This depends on what approach is right for you.

Challenges are a gift.

Am I missing something or is there a certain way you have to plan or approach this process?

I’m originally from Florida so my approach may come across uncertain.

Interesting take on the rental approach.

What were some of the challenges?

So a buy and hold approach would be ideal for me to capitalize on the 1031.