I've done some dedicated spiritbonding of jewelry items (have goldsmith 50) and my observations so far:

1. Item slot doesn't seem to matter as far as the rate goes (at least between the various jewelry slots)
2/4: Spiritbond progresses from monster kill XP, gather item XP, or craft item XP values (and seemingly nothing else. FATE, dungeon completion XP, or quest/leve reward XP don't move it)
3: Higher item level takes more XP to spiritbond