For shipping, you can do a telex release if its by sea. So you don’t need to pay them first but when the goods arrives, you can pay for goods and they will release it. Regarding to paypal, it depends if they have paypal or not

Yes, for express shipment than you will need to pay in full if you are using fedex or ups or dhl. You can speak to your freight forwarder to see if they can provide proof that it has arrived in the country. However, regarding to the amazon warehouse, they need to make a call a few day before to make a booking at Amazon

The accessories are not essential they are included as a bonus so they are not essential to the functionality of the main product, some may use one or more of the accessories others may not - it that makes sense. does it still fall under the criteria “it has to be of the product that you are selling”