3) Dump your samples and other files you want to load in
/Users/you/Documents/VMPC2000XL/Volumes/MPC2000XL. This is also where anything you save will be stored.
Warning: Files in that directory are renamed by the emulator just like on the real 2000XL! This means you shouldn't put the only copy of some important files there. Your data might become corrupted.
4) Report bugs and feature requests here.