Look, there's a gray area here that everyone drives a truck through. Foreigners are able to start companies in America, just not be employed or get paid. Ever wonder why immigrants have small businesses like grocery stores? Because you can buy a store as a foreigner, you can operate it, and you can keep the profits. You just can't be an employee and get paid. Got it?
It's also legal to have a business in Argentina, be an employee of that company, and come to the US to do consulting. I've never figured out exactly how legal it is, but the fact that so many companies, large and small, do this means if it's illegal it must not be very illegal. Every country allows employees to come in and do some work on tourist visas, otherwise each economy would freeze up.
For example, I was a software guy working on a hardware device being produced in China. I ended up going over and spending a week doing integration. On a tourist visa. I was working the entire time, as did all the taiwanese who came over to work with me. There was never a question of anyone getting work visas. I suspect that what we all did was illegal, but it's a gray area and I'm not a lawyer.
The dodge there is we were working for our individual companies, in china, instead of working directly for a chinese company. I've never seen a law that specifies the amount of work where "contracting in country" turns into "employed in country". Not that I know. There's a practical limit, in that at some point an official notices and you get in hot water. I suppose. China's a big country and there are only so many officials. I've done that kind of thing for weeks at a time; no one ever notices at that length.
Couch surfing can be rather pleasant. I've got an empty in-law apartment and a pile of code to write, but I'm writing code this month and next, and don't know if that'll be true past then. You will meet people, you'll learn things. You'll be paid in pizza, red bull, and experience.
If you have a friend with an Argentine-based consulting company, or you can find an Argentine-based consulting company, and say you'll drum up the business when you're in the US but you'll need them to get paid, they'd probably shrug and say "sure", although they'll want to keep part of your paycheck.
Regarding whether you can be part of YC, you should be able to start a company, pick up YC funding, and pay yourself out of the YC funding with a tourist visa. Establishing a corporation provides added ammunition in case you go in front of a judge, where claiming a sole proprietorship looks more like a visa dodge.
What you'll start realizing as you grow older is there's a difference between "management" and "workers". Management gets exceptions. Workers get the shaft. Management is invited across borders, workers are stopped and searched. The largest difference between management and workers is what you call yourself, and how you present yourself.
That's the filter they'll apply to get your US visa in the first place. You have to show enough money to support yourself for the time you'll be here. That's about the same as asking if you're "management" or a "worker".
Sounds annoying to me - if you've got an EU passport, why not just go to the EU? The exchange rate is worse is all. I might recommend Portugal. The country is very polyglot (I was in an office there doing integration and everyone switched to English for me, and they had some UK people in) and there's a number of tech businesses in Lisbon.
Do travel with one nice sports coat and a pair of good shoes, and smile a lot.