Can you work for your own Estonian company, given that you're non-resident? (You can start your own US company, even remotely, but you can't work for it, unless you have Working Visa)
Maybe you mean you can start a US company but not work for it when you are in US on a non-working visa?
Can't see why a US or Estonian company (whether or not you are a director is irrelevant) can't hire you to do some work. Unless you don't have work visa in the country of your stay.
