[RyanW]

Including ifi_aliases.h and ifi_default.h should let you do some things, like assign pwms and digital IOs directly. As for interrupts and the like, our team hasn't figured out how to do those with WPILib yet. We have a project made by taking the default code, adding WPILib, and commenting out everything that gave an error. This should theoretically let you use some of the WPILib functions with default code, but I really doubt ours works and I'm not sure how to get to work in general. It's probably best to stick with either WPILib or the IFI default code.

To get it to show you all the errors at once:
Go to Configure-->Settings, then click on the Projects tab and uncheck "Halt build on first failure".