You contracted there home to purchase it without the willingness or ability to close on it and then you tried selling your contract to a party who also did not have the ways or means to fund it (or is very savvy, saw you are not and delayed on purpose to cut you out of your wholesale commission).

On the construction side I have an advantage because I'm a very experience contractor that can handle multiple big or small projects, specially out of state.I started now because I got all my systems in place!

Looking for the best way to purchase another property with minimal cash up front.

What would be the best piece of advice you could give me? 

Best of luck!

Very old building as well , my client was very strict with how much money he wanted to invest in the building. 

As soon as you get an offer or 10 minutes before the buyer’s agent shows the property?

Use some of that equity to buy another property if you want, but selling I wouldn't say is your best option.

Quote from @Cliff Song: Here's a metaphor.You: "What's the best flooring material for my in-home basketball court?"

Welcome to BiggerPockets Jospeh and best of luck investing!