Bulkloop code available at C:\Cypress\EZ-USB FX3 SDK\1.2\application\c_sharp\bulkloop would be a good reference to understand this. You can refer to http://www.cypress.com/?docID=39952 as well.
Yes, it will work in slave fifo sync mode.
I believe you are talking about a host application (application program) that you may use to talk to your USB device, from the PC. XferData() is an API in CY library provided, that talks to CYUSB3.sys in turn. This can be used to initiate USB transfers, independent of the interface at the P-port (GPIF interface = slave fifo sync in your case). This does not depend on the interface at the P-port of FX3.
You may refer examples of host application provided along with Cypress SuiteUSB (http://www.cypress.com/?rID=57990), in the location "C:\Cypress\Cypress USBSuite\application" after installing USB Suite for Windows.