Everything goes thru the API, but we make it easier for merchants who do not need a complex integration. You can use one of our Plugins, the Payment Widget, or the Hosted Payment Page (and the pre-built code for it) so you won't even realize your using the API. SDK's and sample code are also provided.
The API uses REST with request and responses are formatted as JSON.
Not the actual payment info, but you can store the token and call it again later. Since the consumers payment info is passed directly to us over SSL and never touches your server you never get it to save.
Maybe, though it is not considered part of the normal boarding process. We are happy to answer questions and provide sample code, however if you require extensive coding we would need to discuss your needs. Our Development team would review your request and provide a cost estimate for you. Please open a support ticket or email us with as much detail as you can provide regarding your needs and we will review it and see if we cna be of assitance.