I am an international seller as well and planning to sell in the US with US suppliers. My question: in our case do we have to pay tax? And to be legally selling in the state, do we have to do some paper work, or Just find a supplier and sell our products on let's say our E-store?
No, you don't pay any taxes in the US if you are not located there, you pay your tax in the country you reside in. In regards to paper work, only the paper work involved in opening accounts with your suppliers, nothing else.