Generally you have one set of paperwork per shipment/consignment. I typically include 5 copies of the commercial invoice so that there are plenty to go around.

Generally the couriers/carriers have invoice generation pages available as part of their shipment booking process. Have you asked your carrier?

It depends on how you have booked the shipment - INCOTERMS. Also do you have an account with the carrier or not? It really depends on how you are handling the shipment so will vary.

Most carriers can only facilitate to a person/entity within the destination country unless you ship duty paid. This is why fiscal representatives are often used. I couldn’t tell you the exact process for US FBA - it would probably be worth asking on the US forums as there are likely to be more people doing the same as you.