I agreed to work for a remote client (USA). He had almost no specs defined. Up to a point I kept asking questions to him to derive features but later he grew greedy and kept asking for more and more features.

We exchanged very long emails wherein I tried to explain that I was already stretching myself to meet my ends, and I could only provide certain features agreed before the costs were finalized. 

In this whole process I lost trust that whatever features I am doing work for, I will not get paid for as well. Before 100% payment goal, I have committed all code and shared with him a month before.

Yet he is not well with it - despite code he is trying to find faults with it. As for bugs, he holds final say because I don't own as many hardware as him, and even if I fix things, it's up to him to spell out success / failure. I do not always get his feedback also, yet he keep disapproving my fixes.

I provided him with testable builds but he says code pushed doesn't compile by someone whom he has hired locally!!! I built everything from scratch for him, yet I am supposed to provide support to his team.

He is citing one of my very earlier emails wherein I had promised to deliver features on earlier date (not bug free off course but fully integrated) - the timelines delayed due to his insisting of more and more. As of today, I am not denying any delivery to him but I am not sure I will get paid, and I have taken other clients' work due to him being greedy. So I have suggested him to deliver things later, to which he doesn't agree.

Despite my delivery of features he is citing bugs and threatening to sue me.

Is lawsuit possible & feasible given that:

 - I and him being in different country?
 - The total amount involved is $6K (total paid, hence max disputed)
 - I do not operate as a company but he does. I am self employed freelancer.
 - We do not have any written spec to start with except the wireframes were all provided by him. He didn't spell out the details. I asked as much as I could on skype chat but later on he became too much wanting, so I stopped. He kept thinking that it's my job to derive specs.
 - We neither had any signed contract except for NDA and itemized list of features to deliver (not descriptive list). All other communication has happened through email only.

What are my options here?