HI Tobias,
IOSS have nothing to do with suppling to the USA. IOSS is a scheme exiting only for EU . If you dropship from China, but you do not keep stock in the USA you do not need to form a company there. You may need to register for sales tax when and if you reach an economic nexus in any of the states , but that presumes (depending on the state- rules vary) 100K annual sales or 200 individual sales or even 250 K sales in a particular state,