Welcome to ShipStation! Our Help Center has several articles on insurance that should cover most of your questions. https://help.shipstation.com/hc/en-us/search?utf8=✓&query=insurance&commit=Search
1. Our partner page for Shipsurance covers the terms and limits of their insurance through ShipStation: http://www.shipstation.com/insurance-terms-and-conditions/
2. The carrier/provider (FedEx, UPS, CanadaPost etc) will bill/charge you for the postage printed in ShipStaiton which is why you had to sign up for each of those accounts and enter billing information for each as well. ShipStation will not
bill you for the postage printed and does not cover any of the label fees associated with a carrier/provider. The CC on file with ShipStation is only used for your Subscription Fee and any Shipsurance charges you use.
3. To opt out of the carrier insurance, simply select 'Shipsurance Discount Insurance' under the Insurance field in ShipStation and that's it! Don't forget to put a value in the Insured Amount field too: http://note.io/1PA1FEE
I encourage you to browse our Help Center for any additional starting questions you have about ShipStation. We've tried to cover all the basic questions many of our users ask when first signing up for ShipStation: https://help.shipstation.com/hc/en-us
If you still need some questions answered, feel free to open a support ticket with us and one of our agents will be happy to help!