Taxes: I am not a lawyer, pay a specialist to confirm this part. You fill in either a W-8 BEN (as an individual) or a W-8BEN-E (as a company) and the company keeps this on their records, which basically says "the US has a double taxation treaty with my country so the US co should not withhold taxes", which for most EU countries is in place. You might have to dig through the specific treaty and find the appropriate section that describes withholding percent on the type of income. Search for information regarding those two forms. IIRC Upwork makes service providers fill and send those forms, or used to back in the day.