1) With Amazon seller central, you will need a professional seller account where you can access their bulk upload tool.
You can find steps here: http://www.shoppingcartproductfeed.com/woocommerce-export/amazon-seller-upload/upload-inventory-file-amazon/
2) At this time Amazon does not have an automatic pull (from URL), nor does our plugin have a push-to-Amazon feature. For now you may look at alternatives such as the AMTU program (http://www.amazon.com/gp/help/customer/display.html?nodeId=200779340) which allows you to configure an interval of 15 minutes for example from your own machine. You may also be aware that Amazon provides an API ( https://developer.amazonservices.com/gp/mws/api.html/181-0925533-2007202?ie=UTF8&group=sellers§ion=sellers&version=latest ) where anyone can develop their own push/delivery system, and implementing this feature is definitely on our radar
3) Amazon feeds are generated and uploaded in CSV format.