It was one of my first batches, so I didn't add much, 0.5 oz, or about the zest of 1 lemon. Yeah, I just checked my notes: it was lemon, not orange.
If I were to do it again, I would probably double the amount of zest.
If you want to play it super-safe, do the soaking in vodka. I wouldn't worry about it, though. Lemon zest doesn't strike me as particularly friendly toward micro-organisms.
Just don't heat it or soak it in water. The volatile oils will degrade under heat, and are not water soluble.