How feasible is it to operate your startup in one city (say a European city) but target a different geographical market as the first target market, say the U.S for example?
It happens, but typically you need to spend time in your target market in-person to complete your research, test and validate your assumptions, and to build your sales process. You can return to your home city after your in-person validation steps.
In your case I hope you understand that the US is not a single market. There are at least 5 distinct geographical markets (if not more) in the US that do not behave/respond in the same way to the same product/service offerings. The US is not homogeneous.